WorldWideScience

Sample records for quantum field theoretic

  1. Quantum field theory and coalgebraic logic in theoretical computer science.

    Science.gov (United States)

    Basti, Gianfranco; Capolupo, Antonio; Vitiello, Giuseppe

    2017-11-01

    We suggest that in the framework of the Category Theory it is possible to demonstrate the mathematical and logical dual equivalence between the category of the q-deformed Hopf Coalgebras and the category of the q-deformed Hopf Algebras in quantum field theory (QFT), interpreted as a thermal field theory. Each pair algebra-coalgebra characterizes a QFT system and its mirroring thermal bath, respectively, so to model dissipative quantum systems in far-from-equilibrium conditions, with an evident significance also for biological sciences. Our study is in fact inspired by applications to neuroscience where the brain memory capacity, for instance, has been modeled by using the QFT unitarily inequivalent representations. The q-deformed Hopf Coalgebras and the q-deformed Hopf Algebras constitute two dual categories because characterized by the same functor T, related with the Bogoliubov transform, and by its contravariant application T op , respectively. The q-deformation parameter is related to the Bogoliubov angle, and it is effectively a thermal parameter. Therefore, the different values of q identify univocally, and label the vacua appearing in the foliation process of the quantum vacuum. This means that, in the framework of Universal Coalgebra, as general theory of dynamic and computing systems ("labelled state-transition systems"), the so labelled infinitely many quantum vacua can be interpreted as the Final Coalgebra of an "Infinite State Black-Box Machine". All this opens the way to the possibility of designing a new class of universal quantum computing architectures based on this coalgebraic QFT formulation, as its ability of naturally generating a Fibonacci progression demonstrates. Copyright © 2017 Elsevier Ltd. All rights reserved.

  2. Theoretical physics vol. 2. Quantum mechanics, relativistic quantum mechanics, quantum field theory, elementar-particle theory, thermodynamics and statistics

    International Nuclear Information System (INIS)

    Rebhan, E.

    2005-01-01

    The present second volume treats quantum mechanics, relativistic quantum mechanics, the foundations of quantum-field and elementary-particle theory as well as thermodynamics and statistics. Both volumes comprehend all fields, which are usually offered in a course about theoretical physics. In all treated fields a very careful introduction to the basic natural laws forms the starting point, whereby it is thoroughly analysed, which of them is based on empirics, which is logically deducible, and which role play basic definitions. Extendingly the matter extend of the corresponding courses starting from the relativistic quantum theory an introduction to the elementary particles is developed. All problems are very thoroughly and such extensively studied, that each step is singularly reproducible. On motivation and good understandability is cared much about. The mixing of mathematical difficulties with problems of physical nature often obstructive in the learning is so circumvented, that important mathematical methods are presented in own chapters (for instance Hilbert spaces, Lie groups). By means of many examples and problems (for a large part with solutions) the matter worked out is deepened and exercised. Developments, which are indeed important, but seem for the first approach abandonable, are pursued in excurses. This book starts from courses, which the author has held at the Heinrich-Heine university in Duesseldorf, and was in many repetitions fitted to the requirements of the students. It is conceived in such a way, that it is also after the study suited as dictionary or for the regeneration

  3. Semiclassical and Quantum Field Theoretic Bounds for Traversable Lorentzian Stringy Wormholes

    OpenAIRE

    Nandi, Kamal Kanti; Zhang, Yuan-Zhong; Kumar, K. B. Vijaya

    2004-01-01

    A lower bound on the size of a Lorentzian wormhole can be obtained by semiclassically introducing the Planck cut-off on the magnitude of tidal forces (Horowitz-Ross constraint). Also, an upper bound is provided by the quantum field theoretic constraint in the form of the Ford-Roman Quantum Inequality for massless minimally coupled scalar fields. To date, however, exact static solutions belonging to this scalar field theory have not been worked out to verify these bounds. To fill this gap, we ...

  4. Casimir problem of spherical dielectrics: quantum statistical and field theoretical approaches.

    Science.gov (United States)

    Høye, J S; Brevik, I; Aarseth, J B

    2001-05-01

    The Casimir free energy for a system of two dielectric concentric nonmagnetic spherical bodies is calculated with use of a quantum statistical mechanical method, at arbitrary temperature. By means of this rather novel method, which turns out to be quite powerful (we have shown this to be true in other situations also), we consider first an explicit evaluation of the free energy for the static case, corresponding to zero Matsubara frequency (n=0). Thereafter, the time-dependent case is examined. For comparison we consider the calculation of the free energy with use of the more commonly known field theoretical method, assuming for simplicity metallic boundary surfaces.

  5. A field-theoretic approach to Spin Foam models in Quantum Gravity

    OpenAIRE

    Vitale, Patrizia

    2011-01-01

    We present an introduction to Group Field Theory models, motivating them on the basis of their relationship with discretized BF models of gravity. We derive the Feynmann rules and compute quantum corrections in the coherent states basis.

  6. K theoretical approach to the fusion rules of conformal quantum field theories

    International Nuclear Information System (INIS)

    Recknagel, A.

    1993-09-01

    Conformally invariant quantum field theories are investigated using concepts of the algebraic approach to quantum field theory as well as techniques from the theory of operator algebras. Arguments from the study of statistical lattice models in one and two dimensions, from recent developments in algebraic quantum field theory, and from other sources suggest that there exists and intimate connection between conformal field theories and a special class of C*-algebras, the so-called AF-algebras. For a series of Virasoro minimal models, this correspondence is made explicit by constructing path representations of the irreducible highest weight modules. We then focus on the K 0 -invariant of these path AF-algebras and show how its functorial properties allow to exploit the abstract theory of superselection sectors in order to derive the fusion rules of the W-algebras hidden in the Virasoro minimal models. (orig.)

  7. Proceedings of quantum field theory, quantum mechanics, and quantum optics

    International Nuclear Information System (INIS)

    Dodonov, V.V.; Man; ko, V.I.

    1991-01-01

    This book contains papers presented at the XVIII International Colloquium on Group Theoretical Methods in Physics held in Moscow on June 4-9, 1990. Topics covered include; applications of algebraic methods in quantum field theory, quantum mechanics, quantum optics, spectrum generating groups, quantum algebras, symmetries of equations, quantum physics, coherent states, group representations and space groups

  8. Theoretical physics. Quantum mechanics

    International Nuclear Information System (INIS)

    Rebhan, Eckhard

    2008-01-01

    From the first in two comprehensive volumes appeared Theoretical Physics of the author by this after Mechanics and Electrodynamics also Quantum mechanics appears as thinner single volume. First the illustrative approach via wave mechanics is reproduced. The more abstract Hilbert-space formulation introduces the author later by postulates, which are because of the preceding wave mechanics sufficiently plausible. All concepts of quantum mechanics, which contradict often to the intuitive understanding formed by macroscopic experiences, are extensively discussed and made by means of many examples as well as problems - in the largest part provided with solutions - understandable. To the interpretation of quantum mechanics an extensive special chapter is dedicated. this book arose from courses on theoretical physics, which the author has held at the Heinrich-Heine University in Duesseldorf, and was in numerous repetitions fitted to the requirement of the studyings. it is so designed that it is also after the study suited as reference book or for the renewing. All problems are very thoroughly and such extensively studied that each step is separately reproducible. About motivation and good understandability is cared much

  9. Group theoretical approach to quantum fields in de Sitter space II. The complementary and discrete series

    International Nuclear Information System (INIS)

    Joung, Euihun; Mourad, Jihad; Parentani, Renaud

    2007-01-01

    We use an algebraic approach based on representations of de Sitter group to construct covariant quantum fields in arbitrary dimensions. We study the complementary and the discrete series which correspond to light and massless fields and which lead new feature with respect to the massive principal series we previously studied (hep-th/0606119). When considering the complementary series, we make use of a non-trivial scalar product in order to get local expressions in the position representation. Based on these, we construct a family of covariant canonical fields parametrized by SU(1, 1)/U(1). Each of these correspond to the dS invariant alpha-vacua. The behavior of the modes at asymptotic times brings another difficulty as it is incompatible with the usual definition of the in and out vacua. We propose a generalized notion of these vacua which reduces to the usual conformal vacuum in the conformally massless limit. When considering the massless discrete series we find that no covariant field obeys the canonical commutation relations. To further analyze this singular case, we consider the massless limit of the complementary scalar fields we previously found. We obtain canonical fields with a deformed representation by zero modes. The zero modes have a dS invariant vacuum with singular norm. We propose a regularization by a compactification of the scalar field and a dS invariant definition of the vertex operators. The resulting two-point functions are dS invariant and have a universal logarithmic infrared divergence

  10. Field theoretic renormalization study of reduced quantum electrodynamics and applications to the ultrarelativistic limit of Dirac liquids

    Science.gov (United States)

    Teber, S.; Kotikov, A. V.

    2018-04-01

    The field theoretic renormalization study of reduced quantum electrodynamics (QED) is performed up to two loops. In the condensed matter context, reduced QED constitutes a very natural effective relativistic field theory describing (planar) Dirac liquids, e.g., graphene and graphenelike materials, the surface states of some topological insulators, and possibly half-filled fractional quantum Hall systems. From the field theory point of view, the model involves an effective (reduced) gauge field propagating with a fractional power of the d'Alembertian in marked contrast with usual QEDs. The use of the Bogoliubov-Parasiuk-Hepp-Zimmermann prescription allows for a simple and clear understanding of the structure of the model. In particular, in relation with the ultrarelativistic limit of graphene, we straightforwardly recover the results for both the interaction correction to the optical conductivity C*=(92 -9 π2)/(18 π ) and the anomalous dimension of the fermion field γψ(α ¯ ,ξ )=2 α ¯ (1 -3 ξ )/3 -16 (ζ2NF+4 /27 ) α¯ 2+O (α¯ 3) , where α ¯=e2/(4 π )2 and ξ is the gauge-fixing parameter.

  11. Quantum field theory

    International Nuclear Information System (INIS)

    Mancini, F.

    1986-01-01

    Theoretical physicists, coming from different countries, working on different areas, gathered at Positano: the Proceedings contain all the lectures delivered as well as contributed papers. Many areas of physics are represented, elementary particles in high energy physics, quantum relativity, quantum geometry, condensed matter physics, statistical mechanics; but all works are concerned with the use of the methods of quantum field theory. The first motivation of the meeting was to pay homage to a great physicist and a great friend; it was also an occasion in which theoretical physicists got together to discuss and to compare results in different fields. The meeting was very intimate; the relaxed atmosphere allowed constructive discussions and contributed to a positive exchange of ideas. (orig.)

  12. Quantum field theory

    CERN Document Server

    Mandl, Franz

    2010-01-01

    Following on from the successful first (1984) and revised (1993) editions, this extended and revised text is designed as a short and simple introduction to quantum field theory for final year physics students and for postgraduate students beginning research in theoretical and experimental particle physics. The three main objectives of the book are to: Explain the basic physics and formalism of quantum field theory To make the reader proficient in theory calculations using Feynman diagrams To introduce the reader to gauge theories, which play a central role in elementary particle physic

  13. Studies in quantum field theory

    International Nuclear Information System (INIS)

    Bender, C.M.; Mandula, J.E.; Shrauner, J.E.

    1982-01-01

    Washington University is currently conducting research in many areas of high energy theoretical and mathematical physics. These areas include: strong-coupling approximation; classical solutions of non-Abelian gauge theories; mean-field approximation in quantum field theory; path integral and coherent state representations in quantum field theory; lattice gauge calculations; the nature of perturbation theory in large orders; quark condensation in QCD; chiral symmetry breaking; the l/N expansion in quantum field theory; effective potential and action in quantum field theories, including QCD

  14. Quantum electrodynamics of strong fields

    International Nuclear Information System (INIS)

    Greiner, W.

    1983-01-01

    Quantum Electrodynamics of Strong Fields provides a broad survey of the theoretical and experimental work accomplished, presenting papers by a group of international researchers who have made significant contributions to this developing area. Exploring the quantum theory of strong fields, the volume focuses on the phase transition to a charged vacuum in strong electric fields. The contributors also discuss such related topics as QED at short distances, precision tests of QED, nonperturbative QCD and confinement, pion condensation, and strong gravitational fields In addition, the volume features a historical paper on the roots of quantum field theory in the history of quantum physics by noted researcher Friedrich Hund

  15. Pair production in semiclassical and quantum-field theoretical description; Paarerzeugung in semiklassischer und quantenfeldtheoretischer Beschreibung

    Energy Technology Data Exchange (ETDEWEB)

    Woellert, Anton

    2016-07-27

    Pair production of electron-positron pairs in ultra-intense laser fields is considered in this work. Two regimes are investigated separately. The first regime is the so-called tunnel regime of pair production. The existing tunneling picture which is applicable in this regime will be enhanced by the effects of a magnetic field and an additional, perturbatively treated photon. Both effects are incorporated by the semi-classical approximation. In contrast, no straightforward approach exists so far for the second regime of pair production. Therefore, numerical calculations will be carried out by applying the framework of the in/out-formalism in external fields. These simulations show non-trivial effects that are be expected in this regime. Specifically, the influence of the electromagnetic fields' polarization upon the produced pair spectra is investigated. Furthermore, multi-pair states are studied.

  16. Ultracold quantum fields

    CERN Document Server

    Stoof, Henk T C; Gubbels, Koos

    2009-01-01

    Ultracold Quantum Fields provides a self-contained introduction to quantum field theory for many-particle systems, using functional methods throughout. The general focus is on the behaviour of so-called quantum fluids, i.e., quantum gases and liquids, but trapped atomic gases are always used as an example. Both equilibrium and non-equilibrium phenomena are considered. Firstly, in the equilibrium case, the appropriate Hartree-Fock theory for the properties of a quantum fluid in the normal phase is derived. The focus then turns to the properties in the superfluid phase, and the authors present a microscopic derivation of the Bogoliubov theory of Bose-Einstein condensation and the Bardeen-Cooper-Schrieffer theory of superconductivity. The former is applicable to trapped bosonic gases such as rubidium, lithium, sodium and hydrogen, and the latter in particular to the fermionic isotope of atomic lithium. In the non-equilibrium case, a few topics are discussed for which a field-theoretical approach is especially su...

  17. The theoretical foundations of quantum mechanics

    CERN Document Server

    Baaquie, Belal E

    2013-01-01

    The Theoretical Foundations of Quantum Mechanics addresses fundamental issues that are not discussed in most books on quantum mechanics. This book focuses on analyzing the underlying principles of quantum mechanics and explaining the conceptual and theoretical underpinning of quantum mechanics. In particular, the concepts of quantum indeterminacy, quantum measurement and quantum superposition are analyzed to clarify the concepts that are implicit in the formulation of quantum mechanics. The Schrodinger equation is never solved in the book. Rather, the discussion on the fundamentals of quantum mechanics is treated in a rigorous manner based on the mathematics of quantum mechanics. The new concept of the interplay of empirical and trans-empirical constructs in quantum mechanics is introduced to clarify the foundations of quantum mechanics and to explain the counter-intuitive construction of nature in quantum mechanics. The Theoretical Foundations of Quantum Mechanics is aimed at the advanced undergraduate and a...

  18. Quantum Effects of Electric Fields and Potentials on Electron Motion: An Introduction to Theoretical and Practical Aspects

    Science.gov (United States)

    Matteucci, G.

    2007-01-01

    In the so-called electric Aharonov-Bohm effect, a quantum interference pattern shift is produced when electrons move in an electric field free region but, at the same time, in the presence of a time-dependent electric potential. Analogous fringe shifts are observed in interference experiments where electrons, travelling through an electrostatic…

  19. Theoretical analysis of multiple quantum-well, slow-light devices under applied external fields using a fully analytical model in fractional dimension

    Energy Technology Data Exchange (ETDEWEB)

    Kohandani, R; Kaatuzian, H [Photonics Research Laboratory, Electrical Engineering Department, AmirKabir University of Technology, Hafez Ave., Tehran (Iran, Islamic Republic of)

    2015-01-31

    We report a theoretical study of optical properties of AlGaAs/GaAs multiple quantum-well (MQW), slow-light devices based on excitonic population oscillations under applied external magnetic and electric fields using an analytical model for complex dielectric constant of Wannier excitons in fractional dimension. The results are shown for quantum wells (QWs) of different width. The significant characteristics of the exciton in QWs such as exciton energy and exciton oscillator strength (EOS) can be varied by application of external magnetic and electric fields. It is found that a higher bandwidth and an appropriate slow-down factor (SDF) can be achieved by changing the QW width during the fabrication process and by applying magnetic and electric fields during device functioning, respectively. It is shown that a SDF of 10{sup 5} is obtained at best. (slowing of light)

  20. Digestible quantum field theory

    CERN Document Server

    Smilga, Andrei

    2017-01-01

    This book gives an intermediate level treatment of quantum field theory, appropriate to a reader with a first degree in physics and a working knowledge of special relativity and quantum mechanics. It aims to give the reader some understanding of what QFT is all about, without delving deep into actual calculations of Feynman diagrams or similar. The author serves up a seven‐course menu, which begins with a brief introductory Aperitif. This is followed by the Hors d'oeuvres, which set the scene with a broad survey of the Universe, its theoretical description, and how the ideas of QFT developed during the last century. In the next course, the Art of Cooking, the author recaps on some basic facts of analytical mechanics, relativity, quantum mechanics and also presents some nutritious “extras” in mathematics (group theory at the elementary level) and in physics (theory of scattering). After these preparations, the reader should have a good appetite for the Entrées ‐ the central par t of the book where the...

  1. [Studies in quantum field theory

    International Nuclear Information System (INIS)

    1990-01-01

    During the period 4/1/89--3/31/90 the theoretical physics group supported by Department of Energy Contract No. AC02-78ER04915.A015 and consisting of Professors Bender and Shrauner, Associate Professor Papanicolaou, Assistant Professor Ogilvie, and Senior Research Associate Visser has made progress in many areas of theoretical and mathematical physics. Professors Bender and Shrauner, Associate Professor Papanicolaou, Assistant Professor Ogilvie, and Research Associate Visser are currently conducting research in many areas of high energy theoretical and mathematical physics. These areas include: strong-coupling approximation; classical solutions of non-Abelian gauge theories; mean-field approximation in quantum field theory; path integral and coherent state representations in quantum field theory; lattice gauge calculations; the nature of perturbation theory in large order; quark condensation in QCD; chiral symmetry breaking; the 1/N expansion in quantum field theory; effective potential and action in quantum field theories, including OCD; studies of the early universe and inflation, and quantum gravity

  2. A Field-Theoretical Approach to the P vs. NP Problem via the Phase Sign of Quantum Monte Carlo

    Directory of Open Access Journals (Sweden)

    Andrei T. Patrascu

    2017-10-01

    Full Text Available I present here a new method that allows the introduction of a discrete auxiliary symmetry in a theory in such a way that the eigenvalue spectrum of the fermion functional determinant is made up of complex conjugated pairs. The method implies a particular way of introducing and integrating over auxiliary fields related to a set of artificial shift symmetries. Gauge fixing the artificial continuous shift symmetries in the direct and dual sectors leads to the appearance of direct and dual Becchi–Rouet–Stora–Tyutin (BRST-type global symmetries and of a symplectic structure over the field space. Such a method may allow the extension of the applicability of quantum Monte Carlo methods to some problems plagued by the fermionic sign problem.

  3. Hyperfunction quantum field theory

    International Nuclear Information System (INIS)

    Nagamachi, S.; Mugibayashi, N.

    1976-01-01

    The quantum field theory in terms of Fourier hyperfunctions is constructed. The test function space for hyperfunctions does not contain C infinitely functios with compact support. In spite of this defect the support concept of H-valued Fourier hyperfunctions allows to formulate the locality axiom for hyperfunction quantum field theory. (orig.) [de

  4. Quantum field theory

    International Nuclear Information System (INIS)

    Ryder, L.H.

    1985-01-01

    This introduction to the ideas and techniques of quantum field theory presents the material as simply as possible and is designed for graduate research students. After a brief survey of particle physics, the quantum theory of scalar and spinor fields and then of gauge fields, is developed. The emphasis throughout is on functional methods, which have played a large part in modern field theory. The book concludes with a bridge survey of ''topological'' objects in field theory and assumes a knowledge of quantum mechanics and special relativity

  5. Algebraic quantum field theory

    International Nuclear Information System (INIS)

    Foroutan, A.

    1996-12-01

    The basic assumption that the complete information relevant for a relativistic, local quantum theory is contained in the net structure of the local observables of this theory results first of all in a concise formulation of the algebraic structure of the superselection theory and an intrinsic formulation of charge composition, charge conjugation and the statistics of an algebraic quantum field theory. In a next step, the locality of massive particles together with their spectral properties are wed for the formulation of a selection criterion which opens the access to the massive, non-abelian quantum gauge theories. The role of the electric charge as a superselection rule results in the introduction of charge classes which in term lead to a set of quantum states with optimum localization properties. Finally, the asymptotic observables of quantum electrodynamics are investigated within the framework of algebraic quantum field theory. (author)

  6. Quantum theory of fields

    CERN Document Server

    Wentzel, Gregor

    1949-01-01

    A prominent figure in twentieth-century physics, Gregor Wentzel made major contributions to the development of quantum field theory, first in Europe and later at the University of Chicago. His Quantum Theory of Fields offers a knowledgeable view of the original literature of elementary quantum mechanics and helps make these works accessible to interested readers.An introductory volume rather than an all-inclusive account, the text opens with an examination of general principles, without specification of the field equations of the Lagrange function. The following chapters deal with particular

  7. Euclidean quantum field theory

    International Nuclear Information System (INIS)

    Jaffe, A.

    1985-01-01

    In four seminal papers, written from 1963 to 1968, Kurt Symanzik laid the foundations for his euclidean quantum field theory program (EQFT). His original goal was to use EQFT as a tool to approach the existence question for interacting quantum fields. In 1968, when other methods appeared better suited for the existence question, Symanzik abandoned this heroic attempt and redirected his research toward different questions. (orig./HSI)

  8. Theoretical and quantum mechanics fundamentals for chemists

    CERN Document Server

    Ivanov, Stefan

    2006-01-01

    Provides the basics of theoretical and quantum mechanics in one place and emphasizes the continuity between themUniquely presented to be used for self-taught courses covering theoretical and quantum mechanicsEach chapter includes a detailed outline, a summary, self-assessment questions for which answers can be found in the textInvaluable for chemistry undergraduate and graduate students, chemists, other non-physical scientists, engineering students of modern techniques and technology, specialists who need a better understanding of quantum mechanics.

  9. Designing field-controllable graphene-dot-graphene single molecule switches: A quantum-theoretical proof-of-concept under realistic operating conditions.

    Science.gov (United States)

    Pejov, Ljupčo; Petreska, Irina; Kocarev, Ljupčo

    2015-12-28

    A theoretical proof of the concept that a particularly designed graphene-based moletronics device, constituted by two semi-infinite graphene subunits, acting as source and drain electrodes, and a central benzenoid ring rotator (a "quantum dot"), could act as a field-controllable molecular switch is outlined and analyzed with the density functional theory approach. Besides the ideal (0 K) case, we also consider the operation of such a device under realistic operating (i.e., finite-temperature) conditions. An in-depth insight into the physics behind device controllability by an external field was gained by thorough analyses of the torsional potential of the dot under various conditions (absence or presence of an external gating field with varying strength), computing the torsional correlation time and transition probabilities within the Bloembergen-Purcell-Pound formalism. Both classical and quantum mechanical tunneling contributions to the intramolecular rotation were considered in the model. The main idea that we put forward in the present study is that intramolecular rotors can be controlled by the gating field even in cases when these groups do not possess a permanent dipole moment (as in cases considered previously by us [I. Petreska et al., J. Chem. Phys. 134, 014708-1-014708-12 (2011)] and also by other groups [P. E. Kornilovitch et al., Phys. Rev. B 66, 245413-1-245413-7 (2002)]). Consequently, one can control the molecular switching properties by an external electrostatic field utilizing even nonpolar intramolecular rotors (i.e., in a more general case than those considered so far). Molecular admittance of the currently considered graphene-based molecular switch under various conditions is analyzed employing non-equilibrium Green's function formalism, as well as by analysis of frontier molecular orbitals' behavior.

  10. Unstable Systems and Quantum Zeno Phenomena in Quantum Field Theory

    Science.gov (United States)

    Facchi, P.; Pascazio, S.

    2003-02-01

    We analyze the Zeno phenomenon in quantum field theory. The decay of an unstable system can be modified by changing the time interval between successive measurements (or by varying the coupling to an external system that plays the role of measuring apparatus). We speak of quantum Zeno effect if the decay is slowed and of inverse quantum Zeno (or Heraclitus) effect if it is accelerated. The analysis of the transition between these two regimes requires close scrutiny of the features of the interaction Hamiltonian. We look in detail at quantum field theoretical models of the Lee type.

  11. [Studies in quantum field theory]: Progress report

    International Nuclear Information System (INIS)

    Polmar, S.K.

    1988-01-01

    The theoretical physics group at Washington University has been devoted to the solution of problems in theoretical and mathematical physics. All of the personnel on this task have a similar approach to their research in that they apply sophisticated analytical and numerical techniques to problems primarily in quantum field theory. Specifically, this group has worked on quantum chromodynamics, classical Yang-Mills fields, chiral symmetry breaking condensates, lattice field theory, strong-coupling approximations, perturbation theory in large order, nonlinear waves, 1/N expansions, quantum solitons, phase transitions, nuclear potentials, and early universe calculations

  12. Theoretical physics. Field theory

    International Nuclear Information System (INIS)

    Landau, L.; Lifchitz, E.

    2004-01-01

    This book is the fifth French edition of the famous course written by Landau/Lifchitz and devoted to both the theory of electromagnetic fields and the gravity theory. The talk of the theory of electromagnetic fields is based on special relativity and relates to only the electrodynamics in vacuum and that of pointwise electric charges. On the basis of the fundamental notions of the principle of relativity and of relativistic mechanics, and by using variational principles, the authors develop the fundamental equations of the electromagnetic field, the wave equation and the processes of emission and propagation of light. The theory of gravitational fields, i.e. the general theory of relativity, is exposed in the last five chapters. The fundamentals of the tensor calculus and all that is related to it are progressively introduced just when needed (electromagnetic field tensor, energy-impulse tensor, or curve tensor...). The worldwide reputation of this book is generally allotted to clearness, to the simplicity and the rigorous logic of the demonstrations. (A.C.)

  13. Quantum field theory of fluids.

    Science.gov (United States)

    Gripaios, Ben; Sutherland, Dave

    2015-02-20

    The quantum theory of fields is largely based on studying perturbations around noninteracting, or free, field theories, which correspond to a collection of quantum-mechanical harmonic oscillators. The quantum theory of an ordinary fluid is "freer", in the sense that the noninteracting theory also contains an infinite collection of quantum-mechanical free particles, corresponding to vortex modes. By computing a variety of correlation functions at tree and loop level, we give evidence that a quantum perfect fluid can be consistently formulated as a low-energy, effective field theory. We speculate that the quantum behavior is radically different from both classical fluids and quantum fields.

  14. Theoretical physics 3. Quantum mechanics 1

    International Nuclear Information System (INIS)

    Dreizler, R.M.; Luedde, C.S.

    2008-01-01

    The basic course Theoretical Physics in 5 closed volumes is based on long standing approved courses, in which the preparation of the theoretically physical foundations are in closed form connected with the corresponding matter from mathematics. Interactive web-based problems in html with Applets help the studying in the deepening of the matter: 1 Theoretical Mechanics 2 Electrodynamics and Relativity Theory 3 Quantum Mechanics I 4 Quantum Mechanics II 5 Thermodynamics and Statistical Physics. In this volume the required foundations of quantum mechanics are worked out. Introducting themes are: Fundamental experiments on quantum mechanics, simple quantization methods, matter waves. With the establishment of the Schroedinger equation and the introduction of the operator calculus the way to the first fundamental iece, the discussion and the solution of the Schroedinger equation for one-particle systems is open. The examples discussed there serve as illustrating material for the elaboration of the formal representation theory of quantum mechanics. The theme regions round this introduction to quantum mechanics off: Perturbation theory, spin and angular-momentum questions, and a first view on many-particle problems by means of Coulomb systems like atoms, molecules, and solids [de

  15. Hybrid quantum teleportation: A theoretical model

    Energy Technology Data Exchange (ETDEWEB)

    Takeda, Shuntaro; Mizuta, Takahiro; Fuwa, Maria; Yoshikawa, Jun-ichi; Yonezawa, Hidehiro; Furusawa, Akira [Department of Applied Physics, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)

    2014-12-04

    Hybrid quantum teleportation – continuous-variable teleportation of qubits – is a promising approach for deterministically teleporting photonic qubits. We propose how to implement it with current technology. Our theoretical model shows that faithful qubit transfer can be achieved for this teleportation by choosing an optimal gain for the teleporter’s classical channel.

  16. Particles and quantum fields

    CERN Document Server

    Kleinert, Hagen

    2016-01-01

    This is an introductory book on elementary particles and their interactions. It starts out with many-body Schrödinger theory and second quantization and leads, via its generalization, to relativistic fields of various spins and to gravity. The text begins with the best known quantum field theory so far, the quantum electrodynamics of photon and electrons (QED). It continues by developing the theory of strong interactions between the elementary constituents of matter (quarks). This is possible due to the property called asymptotic freedom. On the way one has to tackle the problem of removing various infinities by renormalization. The divergent sums of infinitely many diagrams are performed with the renormalization group or by variational perturbation theory (VPT). The latter is an outcome of the Feynman-Kleinert variational approach to path integrals discussed in two earlier books of the author, one representing a comprehensive treatise on path integrals, the other dealing with critial phenomena. Unlike ordin...

  17. Quantum Field Theory

    CERN Document Server

    Zeidler, Eberhard

    This is the first volume of a modern introduction to quantum field theory which addresses both mathematicians and physicists ranging from advanced undergraduate students to professional scientists. The book tries to bridge the existing gap between the different languages used by mathematicians and physicists. For students of mathematics it is shown that detailed knowledge of the physical background helps to motivate the mathematical subjects and to discover interesting interrelationships between quite different mathematical topics. For students of physics, fairly advanced mathematics is presented, which is beyond the usual curriculum in physics. It is the author's goal to present the state of the art of realizing Einstein's dream of a unified theory for the four fundamental forces in the universe (gravitational, electromagnetic, strong, and weak interaction). From the reviews: "… Quantum field theory is one of the great intellectual edifices in the history of human thought. … This volume differs from othe...

  18. Quantum electrodynamics in strong external fields

    International Nuclear Information System (INIS)

    Mueller, B.; Rafelski, J.; Kirsch, J.

    1981-05-01

    We review the theoretical description of quantum electrodynamics in the presence of strong and supercritical fields. In particular, the process of the spontaneous vacuum decay accompanied by the observable positron emission in heavy ion collisions is described. Emphasis is put on the proper formulation of many-body aspects in the framework of quantum field theory. The extension of the theory to the description of Bose fields and many-body effects is presented, and the Klein paradox is resolved. Some implications of the theoretical methods developed here are presented concerning non-abelian gauge theories and the quark confinement puzzle. (orig.)

  19. In praise of quantum fields

    International Nuclear Information System (INIS)

    Shirkov, D.V.

    1989-08-01

    A comprehensive discussion of several topics vital for the structure of a modern Quantum Field Theory are discussed, namely: physical content of the notion of a Quantum Field; meaning of infinite renormalization; renormalizability as quantizability; the influence of several principles of quantum nature (quantizability, gauge dynamics, supersymmetry) on quantum fields dynamics; main trends of QFT evolution; present status of QFT and its frontier role in physics. (author). 15 refs, 1 fig

  20. From classical to quantum fields

    CERN Document Server

    Baulieu, Laurent; Sénéor, Roland

    2017-01-01

    Quantum Field Theory has become the universal language of most modern theoretical physics. This introductory textbook shows how this beautiful theory offers the correct mathematical framework to describe and understand the fundamental interactions of elementary particles. The book begins with a brief reminder of basic classical field theories, electrodynamics and general relativity, as well as their symmetry properties, and proceeds with the principles of quantisation following Feynman's path integral approach. Special care is used at every step to illustrate the correct mathematical formulation of the underlying assumptions. Gauge theories and the problems encountered in their quantisation are discussed in detail. The last chapters contain a full description of the Standard Model of particle physics and the attempts to go beyond it, such as grand unified theories and supersymmetry. Written for advanced undergraduate and beginning graduate students in physics and mathematics, the book could also serve as a re...

  1. Moessbauer neutrinos in quantum mechanics and quantum field theory

    International Nuclear Information System (INIS)

    Kopp, Joachim

    2009-01-01

    We demonstrate the correspondence between quantum mechanical and quantum field theoretical descriptions of Moessbauer neutrino oscillations. First, we compute the combined rate Γ of Moessbauer neutrino emission, propagation, and detection in quantum field theory, treating the neutrino as an internal line of a tree level Feynman diagram. We include explicitly the effect of homogeneous line broadening due to fluctuating electromagnetic fields in the source and detector crystals and show that the resulting formula for Γ is identical to the one obtained previously [1] for the case of inhomogeneous line broadening. We then proceed to a quantum mechanical treatment of Moessbauer neutrinos and show that the oscillation, coherence, and resonance terms from the field theoretical result can be reproduced if the neutrino is described as a superposition of Lorentz-shaped wave packet with appropriately chosen energies and widths. On the other hand, the emission rate and the detection cross section, including localization and Lamb-Moessbauer terms, cannot be predicted in quantum mechanics and have to be put in by hand.

  2. Quantum dynamic imaging theoretical and numerical methods

    CERN Document Server

    Ivanov, Misha

    2011-01-01

    Studying and using light or "photons" to image and then to control and transmit molecular information is among the most challenging and significant research fields to emerge in recent years. One of the fastest growing areas involves research in the temporal imaging of quantum phenomena, ranging from molecular dynamics in the femto (10-15s) time regime for atomic motion to the atto (10-18s) time scale of electron motion. In fact, the attosecond "revolution" is now recognized as one of the most important recent breakthroughs and innovations in the science of the 21st century. A major participant in the development of ultrafast femto and attosecond temporal imaging of molecular quantum phenomena has been theory and numerical simulation of the nonlinear, non-perturbative response of atoms and molecules to ultrashort laser pulses. Therefore, imaging quantum dynamics is a new frontier of science requiring advanced mathematical approaches for analyzing and solving spatial and temporal multidimensional partial differ...

  3. Theoretical physics 6 quantum mechanics : basics

    CERN Document Server

    Nolting, Wolfgang

    2017-01-01

    This textbook offers a clear and comprehensive introduction to the basics of quantum mechanics, one of the core components of undergraduate physics courses. It follows on naturally from the previous volumes in this series, thus developing the physical understanding further on to quantized states. The first part of the book introduces wave equations while exploring the Schrödinger equation and the hydrogen atom. More complex themes are covered in the second part of the book, which describes the Dirac formulism of quantum mechanics. Ideally suited to undergraduate students with some grounding in classical mechanics and electrodynamics, the book is enhanced throughout with learning features such as boxed inserts and chapter summaries, with key mathematical derivations highlighted to aid understanding. The text is supported by numerous worked examples and end of chapter problem sets. About the Theoretical Physics series Translated from the renowned and highly successful German editions, the eight volumes of this...

  4. Wilson lines in quantum field theory

    CERN Document Server

    Cherednikov, Igor O; Veken, Frederik F van der

    2014-01-01

    The objective of this book is to get the reader acquainted with theoretical and mathematical foundations of the concept of Wilson loops in the context of modern quantum field theory. It teaches how to perform independently with some elementary calculations on Wilson lines, and shows the recent development of the subject in different important areas of research.

  5. Partially reversible quantum operations and their information-theoretical properties

    CERN Document Server

    Ban, M

    2003-01-01

    Partial reversibility of quantum operations (or quantum channels) is considered from the information-theoretical point of view. The necessary and sufficient condition for quantum operations to be partially reversible is shown. The condition can be expressed in terms of information-theoretical quantities (von Neumann entropy and PSI-information). The quantum information-theoretical meanings of the condition are discussed. The results are compared with those obtained for completely reversible quantum operations. The PSI-information is calculated for the quantum depolarizing channel of a qubit and the linear dissipative channel of a single-mode bosonic system.

  6. Quantum field theory of universe

    International Nuclear Information System (INIS)

    Hosoya, Akio; Morikawa, Masahiro.

    1988-08-01

    As is well-known, the wave function of universe dictated by the Wheeler-DeWitt equation has a difficulty in its probabilistic interpretation. In order to overcome this difficulty, we explore a theoretical possibility of the second quantization of universe, following the same passage historically taken for the Klein-Gordon particles and the Nambu-Goto strings. It turns out that multiple production of universes is an inevitable consequence even if the initial state is nothing. The problematical interpretation of wave function of universe is circumvented by introducing an internal comoving model detector, which is an analogue of the DeWitt-Unruh detector in the quantum field theory in curved space-time. (author)

  7. Information-theoretic temporal Bell inequality and quantum computation

    International Nuclear Information System (INIS)

    Morikoshi, Fumiaki

    2006-01-01

    An information-theoretic temporal Bell inequality is formulated to contrast classical and quantum computations. Any classical algorithm satisfies the inequality, while quantum ones can violate it. Therefore, the violation of the inequality is an immediate consequence of the quantumness in the computation. Furthermore, this approach suggests a notion of temporal nonlocality in quantum computation

  8. Models of Quantum Space Time: Quantum Field Planes

    OpenAIRE

    Mack, G.; Schomerus, V.

    1994-01-01

    Quantum field planes furnish a noncommutative differential algebra $\\Omega$ which substitutes for the commutative algebra of functions and forms on a contractible manifold. The data required in their construction come from a quantum field theory. The basic idea is to replace the ground field ${\\bf C}$ of quantum planes by the noncommutative algebra ${\\cal A}$ of observables of the quantum field theory.

  9. Signatures of Quantum Phase Transitions via Quantum Information Theoretic Measures

    Science.gov (United States)

    Bose, I.; Tribedi, A.

    Quantum phase transitions (QPTs) in many body systems occur at T = 0 brought about by tuning a non-thermal parameter, e.g. pressure, chemical composition or external magnetic field [1, 2]. In a QPT, the ground state wave function undergoes qualitative changes at the transition point. The transition is driven by quantum fluctuations whereas ordinary phase transitions occurring at nonzero temperatures are driven by thermal fluctuations. Like a thermal phase transition, a QPT can be first order, second order or higher order. The thermal critical point, associated with a second-order phase transition, is characterized by the presence of thermal fluctuations on all length scales resulting in a divergent correlation length. The free energy and the thermodynamic functions develop singularities as temperature Trightarrow T_{textrm{c}} , the critical temperature. At the quantum critical point (QCP), quantum fluctuations occur on all length scales leading to a divergent correlation length. The ground state and related physical quantities become non-analytic as the tuning parameter g tends to the critical value g c . The influence of QPTs extends into the finite T part of the phase diagram so that experimental detection of QPTs is possible.

  10. Quantum principles in field interactions

    International Nuclear Information System (INIS)

    Shirkov, D.V.

    1986-01-01

    The concept of quantum principle is intruduced as a principle whosee formulation is based on specific quantum ideas and notions. We consider three such principles, viz. those of quantizability, local gauge symmetry, and supersymmetry, and their role in the development of the quantum field theory (QFT). Concerning the first of these, we analyze the formal aspects and physical contents of the renormalization procedure in QFT and its relation to ultraviolet divergences and the renorm group. The quantizability principle is formulated as an existence condition of a self-consistent quantum version with a given mechanism of the field interaction. It is shown that the consecutive (from a historial point of view) use of these quantum principles puts still larger limitations on possible forms of field interactions

  11. Knots, topology and quantum field theories

    International Nuclear Information System (INIS)

    Lusanna, L.

    1989-01-01

    The title of the workshop, Knots, Topology and Quantum Field Theory, accurate reflected the topics discussed. There have been important developments in mathematical and quantum field theory in the past few years, which had a large impact on physicist thinking. It is historically unusual and pleasing that these developments are taking place as a result of an intense interaction between mathematical physicists and mathematician. On the one hand, topological concepts and methods are playing an increasingly important lead to novel mathematical concepts: for instance, the study of quantum groups open a new chapter in the deformation theory of Lie algebras. These developments at present will lead to new insights into the theory of elementary particles and their interactions. In essence, the talks dealt with three, broadly defined areas of theoretical physics. One was topological quantum field theories, the other the problem of quantum groups and the third one certain aspects of more traditional field theories, such as, for instance, quantum gravity. These topics, however, are interrelated and the general theme of the workshop defies rigid classification; this was evident from the cross references to be found in almo all the talks

  12. Theory of interacting quantum fields

    International Nuclear Information System (INIS)

    Rebenko, Alexei L.

    2012-01-01

    This monograph is devoted to the systematic presentation of foundations of the quantum field theory. Unlike numerous monographs devoted to this topic, a wide range of problems covered in this book are accompanied by their sufficiently clear interpretations and applications. An important significant feature of this monograph is the desire of the author to present mathematical problems of the quantum field theory with regard to new methods of the constructive and Euclidean field theory that appeared in the last thirty years of the 20 th century and are based on the rigorous mathematical apparatus of functional analysis, the theory of operators, and the theory of generalized functions. The monograph is useful for students, post-graduate students, and young scientists who desire to understand not only the formality of construction of the quantum field theory but also its essence and connection with the classical mechanics, relativistic classical field theory, quantum mechanics, group theory, and the theory of path integral formalism.

  13. Dirac, Jordan and quantum fields

    International Nuclear Information System (INIS)

    Darrigol, O.

    1985-01-01

    The case of two principal physicists of quantum mechanics is specially chose: Paul Dirac and Pascual Jordan. They gave a signification and an importance very different to the notion of quantum field, and in particular to the quantized matter wave one. Through their formation and motivation differences, such as they are expressed in their writings, this deep difference is tentatively understood [fr

  14. Topological quantum field theory and four manifolds

    CERN Document Server

    Marino, Marcos

    2005-01-01

    The present book is the first of its kind in dealing with topological quantum field theories and their applications to topological aspects of four manifolds. It is not only unique for this reason but also because it contains sufficient introductory material that it can be read by mathematicians and theoretical physicists. On the one hand, it contains a chapter dealing with topological aspects of four manifolds, on the other hand it provides a full introduction to supersymmetry. The book constitutes an essential tool for researchers interested in the basics of topological quantum field theory, since these theories are introduced in detail from a general point of view. In addition, the book describes Donaldson theory and Seiberg-Witten theory, and provides all the details that have led to the connection between these theories using topological quantum field theory. It provides a full account of Witten’s magic formula relating Donaldson and Seiberg-Witten invariants. Furthermore, the book presents some of the ...

  15. Quantum Field Theory in (0 + 1) Dimensions

    Science.gov (United States)

    Boozer, A. D.

    2007-01-01

    We show that many of the key ideas of quantum field theory can be illustrated simply and straightforwardly by using toy models in (0 + 1) dimensions. Because quantum field theory in (0 + 1) dimensions is equivalent to quantum mechanics, these models allow us to use techniques from quantum mechanics to gain insight into quantum field theory. In…

  16. Theoretical modeling of large molecular systems. Advances in the local self consistent field method for mixed quantum mechanics/molecular mechanics calculations.

    Science.gov (United States)

    Monari, Antonio; Rivail, Jean-Louis; Assfeld, Xavier

    2013-02-19

    Molecular mechanics methods can efficiently compute the macroscopic properties of a large molecular system but cannot represent the electronic changes that occur during a chemical reaction or an electronic transition. Quantum mechanical methods can accurately simulate these processes, but they require considerably greater computational resources. Because electronic changes typically occur in a limited part of the system, such as the solute in a molecular solution or the substrate within the active site of enzymatic reactions, researchers can limit the quantum computation to this part of the system. Researchers take into account the influence of the surroundings by embedding this quantum computation into a calculation of the whole system described at the molecular mechanical level, a strategy known as the mixed quantum mechanics/molecular mechanics (QM/MM) approach. The accuracy of this embedding varies according to the types of interactions included, whether they are purely mechanical or classically electrostatic. This embedding can also introduce the induced polarization of the surroundings. The difficulty in QM/MM calculations comes from the splitting of the system into two parts, which requires severing the chemical bonds that link the quantum mechanical subsystem to the classical subsystem. Typically, researchers replace the quantoclassical atoms, those at the boundary between the subsystems, with a monovalent link atom. For example, researchers might add a hydrogen atom when a C-C bond is cut. This Account describes another approach, the Local Self Consistent Field (LSCF), which was developed in our laboratory. LSCF links the quantum mechanical portion of the molecule to the classical portion using a strictly localized bond orbital extracted from a small model molecule for each bond. In this scenario, the quantoclassical atom has an apparent nuclear charge of +1. To achieve correct bond lengths and force constants, we must take into account the inner shell of

  17. Topics in quantum field theory

    International Nuclear Information System (INIS)

    Svaiter, N.F.

    2006-11-01

    This paper presents some important aspects on quantum field theory, covering the following aspects: the triumph and limitations of the quantum field theory; the field theory in curved spaces - Hawking and Unruh-Davies effects; the problem of divergent theory of the zero-point; the problem of the spinning detector and the Trocheries-Takeno vacuum; the field theory at finite temperature - symmetry breaking and phase transition; the problem of the summability of the perturbative series and the perturbative expansion for the strong coupling; quantized fields in presence of classical macroscopic structures; the Parisi-Wu stochastic quantization method

  18. A group theoretic approach to quantum information

    CERN Document Server

    Hayashi, Masahito

    2017-01-01

    This textbook is the first one addressing quantum information from the viewpoint of group symmetry. Quantum systems have a group symmetrical structure. This structure enables to handle systematically quantum information processing. However, there is no other textbook focusing on group symmetry for quantum information although there exist many textbooks for group representation. After the mathematical preparation of quantum information, this book discusses quantum entanglement and its quantification by using group symmetry. Group symmetry drastically simplifies the calculation of several entanglement measures although their calculations are usually very difficult to handle. This book treats optimal information processes including quantum state estimation, quantum state cloning, estimation of group action and quantum channel etc. Usually it is very difficult to derive the optimal quantum information processes without asymptotic setting of these topics. However, group symmetry allows to derive these optimal solu...

  19. Quantum groups, quantum categories and quantum field theory

    CERN Document Server

    Fröhlich, Jürg

    1993-01-01

    This book reviews recent results on low-dimensional quantum field theories and their connection with quantum group theory and the theory of braided, balanced tensor categories. It presents detailed, mathematically precise introductions to these subjects and then continues with new results. Among the main results are a detailed analysis of the representation theory of U (sl ), for q a primitive root of unity, and a semi-simple quotient thereof, a classfication of braided tensor categories generated by an object of q-dimension less than two, and an application of these results to the theory of sectors in algebraic quantum field theory. This clarifies the notion of "quantized symmetries" in quantum fieldtheory. The reader is expected to be familiar with basic notions and resultsin algebra. The book is intended for research mathematicians, mathematical physicists and graduate students.

  20. Embedding classical fields in quantum field theories

    International Nuclear Information System (INIS)

    Blaha, S.

    1978-01-01

    We describe a procedure for quantizing a classical field theory which is the field-theoretica analog of Sudarshan's method for embedding a classical-mechanical system in a quantum-mechanical system. The essence of the difference between our quantization procedure and Fock-space quantization lies in the choice of vacuum states. The key to our choice of vacuum is the procedure we outline for constructing Lagrangians which have gradient terms linear in the field varialbes from classical Lagrangians which have gradient terms which are quadratic in field variables. We apply this procedure to model electrodynamic field theories, Yang-Mills theories, and a vierbein model of gravity. In the case of electrodynamics models we find a formalism with a close similarity to the coherent-soft-photon-state formalism of QED. In addition, photons propagate to t = + infinity via retarded propagators. We also show how to construct a quantum field for action-at-a-distance electrodynamics. In the Yang-Mills case we show that a previously suggested model for quark confinement necessarily has gluons with principle-value propagation which allows the model to be unitary despite the presence of higher-order-derivative field equations. In the vierbein-gravity model we show that our quantization procedure allows us to treat the classical and quantum parts of the metric field in a unified manner. We find a new perturbation scheme for quantum gravity as a result

  1. From quantum gravity to quantum field theory via noncommutative geometry

    International Nuclear Information System (INIS)

    Aastrup, Johannes; Grimstrup, Jesper Møller

    2014-01-01

    A link between canonical quantum gravity and fermionic quantum field theory is established in this paper. From a spectral triple construction, which encodes the kinematics of quantum gravity, we construct semi-classical states which, in a semi-classical limit, give a system of interacting fermions in an ambient gravitational field. The emergent interaction involves flux tubes of the gravitational field. In the additional limit, where all gravitational degrees of freedom are turned off, a free fermionic quantum field theory emerges. (paper)

  2. 1. Vienna central european seminar on particle physics and quantum field theory. Advances in quantum field theory. Program

    International Nuclear Information System (INIS)

    Hueffel, H.

    2004-01-01

    The new seminar series 'Vienna central European seminar on particle physics and quantum field theory' has been created 2004 and is intended to provide interactions between leading researchers and junior physicists. This year 'Advances in quantum field theory' has been chosen as subject and is centred on field theoretic aspects of string dualities. The lectures mainly focus on these aspects of string dualities. Further lectures regarding supersymmetric gauge theories, quantum gravity and noncommutative field theory are presented. The vast field of research concerning string dualities justifies special attention to their effects on field theory. (author)

  3. Towards the mathematics of quantum field theory

    CERN Document Server

    Paugam, Frédéric

    2014-01-01

    The aim of this book is to introduce mathematicians (and, in particular, graduate students) to the mathematical methods of theoretical and experimental quantum field theory, with an emphasis on coordinate-free presentations of the mathematical objects in play. This should in turn promote interaction between mathematicians and physicists by supplying a common and flexible language for the good of both communities, even if the mathematical one is the primary target. This reference work provides a coherent and complete mathematical toolbox for classical and quantum field theory, based on categorical and homotopical methods, representing an original contribution to the literature. The first part of the book introduces the mathematical methods needed to work with the physicists' spaces of fields, including parameterized and functional differential geometry, functorial analysis, and the homotopical geometric theory of non-linear partial differential equations, with applications to general gauge theories. The second...

  4. Lectures on quantum field theory

    CERN Document Server

    Das, Ashok

    2008-01-01

    This book consists of the lectures for a two-semester course on quantum field theory, and as such is presented in a quite informal and personal manner. The course starts with relativistic one-particle systems, and develops the basics of quantum field theory with an analysis of the representations of the Poincaré group. Canonical quantization is carried out for scalar, fermion, Abelian and non-Abelian gauge theories. Covariant quantization of gauge theories is also carried out with a detailed description of the BRST symmetry. The Higgs phenomenon and the standard model of electroweak interactio

  5. Introduction to quantum field theory

    International Nuclear Information System (INIS)

    Kazakov, D.I.

    1988-01-01

    The lectures appear to be a continuation to the introduction to elementary principles of the quantum field theory. The work is aimed at constructing the formalism of standard particle interaction model. Efforts are made to exceed the limits of the standard model in the quantum field theory context. Grand unification models including strong and electrical weak interactions, supersymmetric generalizations of the standard model and grand unification theories and, finally, supergravitation theories including gravitation interaction to the universal scheme, are considered. 3 refs.; 19 figs.; 2 tabs

  6. Observer dependence of quantum states in relativistic quantum field theories

    International Nuclear Information System (INIS)

    Malin, S.

    1982-01-01

    Quantum states can be understood as either (i) describing quantum systems or (ii) representing observers' knowledge about quantum systems. These different meanings are shown to imply different transformation properties in relativistic field theories. The rules for the reduction of quantum states and the transformation properties of quantum states under Lorentz transformations are derived for case (ii). The results obtained are applied to a quantum system recently presented and analyzed by Aharonov and Albert. It is shown that the present results, combined with Aharonov and Albert's, amount to a proof of Bohr's view that quantum states represent observers' knowledge about quantum systems

  7. String-localized quantum fields

    International Nuclear Information System (INIS)

    Mund, Jens; Santos, Jose Amancio dos; Silva, Cristhiano Duarte; Oliveira, Erichardson de

    2009-01-01

    Full text. The principles of physics admit (unobservable) quantum fields which are localized not on points, but on strings in the sense of Mandelstam: a string emanates from a point in Minkowski space and extends to infinity in some space-like direction. This type of localization might permit the construction of new models, for various reasons: (a) in general, weaker localization implies better UV behaviour. Therefore, the class of renormalizable interactions in the string-localized has a chance to be larger than in the point-localized case; (b) for certain particle types, there are no point-localized (free) quantum fields - for example Anyons in d = 2 + 1, and Wigner's massless 'infinite spin' particles. For the latter, free string-localized quantum fields have been constructed; (c) in contrast to the point-localized case, string-localization admits covariant vector/tensor potentials for fotons and gravitons in a Hilbert space representation with positive energy. We shall present free string-localized quantum fields for various particle types, and some ideas about the perturbative construction of interacting string-localized fields. A central point will be an analogue of gauge theories, completely within a Hilbert space and without ghosts, trading gauge dependence with dependence on the direction of the localization string. In order to discuss renormalizability (item (a)), methods from microlocal analysis (wave front set and scaling degree) are needed. (author)

  8. The quantum double in integrable quantum field theory

    International Nuclear Information System (INIS)

    Bernard, D.; LeClair, A.

    1993-01-01

    Various aspects of recent works on affine quantum group symmetry of integrable 2D quantum field theory are reviewed and further clarified. A geometrical meaning is given to the quantum double, and other properties of quantum groups. The S-matrix is identified with the universal R-matrix. Multiplicative presentations of the yangian double are analyzed. (orig.)

  9. Electric fields and quantum wormholes

    NARCIS (Netherlands)

    Engelhardt, D.; Freivogel, B.; Iqbal, N.

    2015-01-01

    Electric fields can thread a classical Einstein-Rosen bridge. Maldacena and Susskind have recently suggested that in a theory of dynamical gravity the entanglement of ordinary perturbative quanta should be viewed as creating a quantum version of an Einstein-Rosen bridge between the particles, or a

  10. Braided quantum field theories and their symmetries

    International Nuclear Information System (INIS)

    Sasai, Yuya; Sasakura, Naoki

    2007-01-01

    Braided quantum field theories, proposed by Oeckl, can provide a framework for quantum field theories that possess Hopf algebra symmetries. In quantum field theories, symmetries lead to non-perturbative relations among correlation functions. We study Hopf algebra symmetries and such relations in the context of braided quantum field theories. We give the four algebraic conditions among Hopf algebra symmetries and braided quantum field theories that are required for the relations to hold. As concrete examples, we apply our analysis to the Poincare symmetries of two examples of noncommutative field theories. One is the effective quantum field theory of three-dimensional quantum gravity coupled to spinless particles formulated by Freidel and Livine, and the other is noncommutative field theory on the Moyal plane. We also comment on quantum field theory in κ-Minkowski spacetime. (author)

  11. Introduction to quantum field theory

    CERN Document Server

    Chang, Shau-Jin

    1990-01-01

    This book presents in a short volume the basics of quantum field theory and many body physics. The first part introduces the perturbative techniques without sophisticated apparatus and applies them to numerous problems including quantum electrodynamics (renormalization), Fermi and Bose gases, the Brueckner theory of nuclear system, liquid Helium and classical systems with noise. The material is clear, illustrative and the important points are stressed to help the reader get the understanding of what is crucial without overwhelming him with unnecessary detours or comments. The material in the s

  12. A theoretical study of exciton energy levels in laterally coupled quantum dots

    International Nuclear Information System (INIS)

    Barticevic, Z; Pacheco, M; Duque, C A; Oliveira, L E

    2009-01-01

    A theoretical study of the electronic and optical properties of laterally coupled quantum dots, under applied magnetic fields perpendicular to the plane of the dots, is presented. The exciton energy levels of such laterally coupled quantum-dot systems, together with the corresponding wavefunctions and eigenvalues, are obtained in the effective-mass approximation by using an extended variational approach in which the magnetoexciton states are simultaneously obtained. One achieves the expected limits of one single quantum dot, when the distance between the dots is zero, and of two uncoupled quantum dots, when the distance between the dots is large enough. Moreover, present calculations-with appropriate structural dimensions of the two-dot system-are shown to be in agreement with measurements in self-assembled laterally aligned GaAs quantum-dot pairs and naturally/accidentally occurring coupled quantum dots in GaAs/GaAlAs quantum wells.

  13. Information theoretic resources in quantum theory

    Science.gov (United States)

    Meznaric, Sebastian

    Resource identification and quantification is an essential element of both classical and quantum information theory. Entanglement is one of these resources, arising when quantum communication and nonlocal operations are expensive to perform. In the first part of this thesis we quantify the effective entanglement when operations are additionally restricted to account for both fundamental restrictions on operations, such as those arising from superselection rules, as well as experimental errors arising from the imperfections in the apparatus. For an important class of errors we find a linear relationship between the usual and effective higher dimensional generalization of concurrence, a measure of entanglement. Following the treatment of effective entanglement, we focus on a related concept of nonlocality in the presence of superselection rules (SSR). Here we propose a scheme that may be used to activate nongenuinely multipartite nonlocality, in that a single copy of a state is not multipartite nonlocal, while two or more copies exhibit nongenuinely multipartite nonlocality. The states used exhibit the more powerful genuinely multipartite nonlocality when SSR are not enforced, but not when they are, raising the question of what is needed for genuinely multipartite nonlocality. We show that whenever the number of particles is insufficient, the degrading of genuinely multipartite to nongenuinely multipartite nonlocality is necessary. While in the first few chapters we focus our attention on understanding the resources present in quantum states, in the final part we turn the picture around and instead treat operations themselves as a resource. We provide our observers with free access to classical operations - ie. those that cannot detect or generate quantum coherence. We show that the operation of interest can then be used to either generate or detect quantum coherence if and only if it violates a particular commutation relation. Using the relative entropy, the

  14. Quantum wormhole with spinor field

    International Nuclear Information System (INIS)

    Wang Wenfu; Tao Caide

    1994-01-01

    Using the Hawking-Page boundary condition, we discuss the quantum wormhole with spinor field. The corresponding Wheeler-De Witt equation is derived, and the wave function of the wormhole calculated. After analysing the wormhole's wave function, the authors found that the probability density of the wormhole appearing at a = 0 is zero, and the minimal radius of the wormhole is on the Planck scale

  15. Quantum electrodynamical corrections in critical fields

    International Nuclear Information System (INIS)

    Soff, G.

    1990-09-01

    We investigate field-theoretical corrections, such as vacuum polarization and self energy to study their influence on strongly bound electrons in heavy and superheavy atoms. In critical fields (Z≅170) for spontaneous e + e - pair creation the coupling constant of the external field Zα exceeds 1 thereby preventing the ordinary perturbative approach of quantum electrodynamical correction which employs an expansion in Zα. For heavy and superheavy elements radiative corrections have to be treated to all orders in Zα. The dominant effect is provided by the Uehling contribution being visualized by the first diagram on the right hand side. It is linear in the external field and thus of order α(Zα). (orig./HSI)

  16. Spectral methods in quantum field theory and quantum cosmology

    Science.gov (United States)

    Esposito, Giampiero; Fucci, Guglielmo; Kamenshchik, Alexander Yu; Kirsten, Klaus

    2012-09-01

    We review the application of the spectral zeta function to the one-loop properties of quantum field theories on manifolds with boundary, with emphasis on Euclidean quantum gravity and quantum cosmology. As was shown in the literature some time ago, the only boundary conditions that are completely invariant under infinitesimal diffeomorphisms on metric perturbations suffer from a drawback, i.e. lack of strong ellipticity of the resulting boundary-value problem. Nevertheless, at least on the Euclidean 4-ball background, it remains possible to evaluate the ζ(0) value, which describes in this case a universe which, in the limit of small 3-geometry, has vanishing probability of approaching the cosmological singularity. An assessment of this result is performed here, discussing its physical and mathematical implications. This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical in honour of Stuart Dowker’s 75th birthday devoted to ‘Applications of zeta functions and other spectral functions in mathematics and physics’.

  17. Quantum fields on the computer

    CERN Document Server

    1992-01-01

    This book provides an overview of recent progress in computer simulations of nonperturbative phenomena in quantum field theory, particularly in the context of the lattice approach. It is a collection of extensive self-contained reviews of various subtopics, including algorithms, spectroscopy, finite temperature physics, Yukawa and chiral theories, bounds on the Higgs meson mass, the renormalization group, and weak decays of hadrons.Physicists with some knowledge of lattice gauge ideas will find this book a useful and interesting source of information on the recent developments in the field.

  18. A philosophical approach to quantum field theory

    CERN Document Server

    Öttinger, Hans Christian

    2015-01-01

    This text presents an intuitive and robust mathematical image of fundamental particle physics based on a novel approach to quantum field theory, which is guided by four carefully motivated metaphysical postulates. In particular, the book explores a dissipative approach to quantum field theory, which is illustrated for scalar field theory and quantum electrodynamics, and proposes an attractive explanation of the Planck scale in quantum gravity. Offering a radically new perspective on this topic, the book focuses on the conceptual foundations of quantum field theory and ontological questions. It also suggests a new stochastic simulation technique in quantum field theory which is complementary to existing ones. Encouraging rigor in a field containing many mathematical subtleties and pitfalls this text is a helpful companion for students of physics and philosophers interested in quantum field theory, and it allows readers to gain an intuitive rather than a formal understanding.

  19. A philosophical approach to quantum field theory

    CERN Document Server

    Öttinger, Hans Christian

    2017-01-01

    This text presents an intuitive and robust mathematical image of fundamental particle physics based on a novel approach to quantum field theory, which is guided by four carefully motivated metaphysical postulates. In particular, the book explores a dissipative approach to quantum field theory, which is illustrated for scalar field theory and quantum electrodynamics, and proposes an attractive explanation of the Planck scale in quantum gravity. Offering a radically new perspective on this topic, the book focuses on the conceptual foundations of quantum field theory and ontological questions. It also suggests a new stochastic simulation technique in quantum field theory which is complementary to existing ones. Encouraging rigor in a field containing many mathematical subtleties and pitfalls this text is a helpful companion for students of physics and philosophers interested in quantum field theory, and it allows readers to gain an intuitive rather than a formal understanding.

  20. Quantum mechanics of Proca fields

    International Nuclear Information System (INIS)

    Zamani, Farhad; Mostafazadeh, Ali

    2009-01-01

    We construct the most general physically admissible positive-definite inner product on the space of Proca fields. Up to a trivial scaling this defines a five-parameter family of Lorentz invariant inner products that we use to construct a genuine Hilbert space for the quantum mechanics of Proca fields. If we identify the generator of time translations with the Hamiltonian, we obtain a unitary quantum system that describes first-quantized Proca fields and does not involve the conventional restriction to the positive-frequency fields. We provide a rather comprehensive analysis of this system. In particular, we examine the conserved current density responsible for the conservation of the probabilities, explore the global gauge symmetry underlying the conservation of the probabilities, obtain a probability current density, construct position, momentum, helicity, spin, and angular momentum operators, and determine the localized Proca fields. We also compute the generalized parity (P), generalized time-reversal (T), and generalized charge or chirality (C) operators for this system and offer a physical interpretation for its PT-, C-, and CPT-symmetries.

  1. A short course in quantum information theory an approach from theoretical physics

    CERN Document Server

    Diosi, Lajos

    2011-01-01

    This short and concise primer takes the vantage point of theoretical physics and the unity of physics. It sets out to strip the burgeoning field of quantum information science to its basics by linking it to universal concepts in physics. An extensive lecture rather than a comprehensive textbook, this volume is based on courses delivered over several years to advanced undergraduate and beginning graduate students, but essentially it addresses anyone with a working knowledge of basic quantum physics. Readers will find these lectures a most adequate entry point for theoretical studies in this field. For the second edition, the authors has succeeded in adding many new topics while sticking to the conciseness of the overall approach. A new chapter on qubit thermodynamics has been added, while new sections and subsections have been incorporated in various chapter to deal with weak and time-continuous measurements, period-finding quantum algorithms and quantum error corrections. From the reviews of the first edition...

  2. Beyond Quantum Fields: A Classical Fields Approach to QED

    Directory of Open Access Journals (Sweden)

    Chafin C.

    2015-07-01

    Full Text Available A classical field theory is introduced that is defined on a tower of dimensionally in- creasing spaces and is argued to be equivalent to QED. The domain of dependence is discussed to show how an equal times picture of the many coordinate space gives QED results as part of a well posed initial value formalism. Identical particle symmetries are not, a priori, required but when introduced are clearly propagated. This construc- tion uses only classical fields to provide some explanation for why quantum fields and canonical commutation results have been successful. Some old and essential questions regarding causality of propagators are resolved. The problem of resummation, gener- ally forbidden for conditionally convergent series, is dis cussed from the standpoint of particular truncations of the infinite tower of functions an d a two step adiabatic turn on for scattering. As a result of this approach it is shown that the photon inherits its quantization ~ ω from the free lagrangian of the Dirac electrons despite the fact that the free electromagnetic lagrangian has no ~ in it. This provides a possible explanation for the canonical commutation relations for quantum operators , [ ˆ P , ˆ Q ] = i ~ , without ever needing to invoke such a quantum postulate. The form of the equal times conservation laws in this many particle field theory suggests a simplification of the radiation reaction process for fields that allows QED to arise from a sum of path integrals in the various particle time coordinates. A novel method of unifying this theory with gravity, but that has no obvious quantum field theoretic computational scheme , is introduced.

  3. Mathematical aspects of field quantization. Quantum electrodynamics

    International Nuclear Information System (INIS)

    Bongaarts, P.J.M.

    1983-01-01

    Fundamental mathematical aspects of quantum field theory are discussed. A brief review of various approaches to mathematical problems of quantum electrodynamics is given, preceded by a more extensive account of the development of ideas on the mathematical nature of quantum fields in general, providing an appropriate historical context. (author)

  4. Quantum Field Theory A Modern Perspective

    CERN Document Server

    Parameswaran Nair, V

    2005-01-01

    Quantum field theory, which started with Paul Dirac’s work shortly after the discovery of quantum mechanics, has produced an impressive and important array of results. Quantum electrodynamics, with its extremely accurate and well-tested predictions, and the standard model of electroweak and chromodynamic (nuclear) forces are examples of successful theories. Field theory has also been applied to a variety of phenomena in condensed matter physics, including superconductivity, superfluidity and the quantum Hall effect. The concept of the renormalization group has given us a new perspective on field theory in general and on critical phenomena in particular. At this stage, a strong case can be made that quantum field theory is the mathematical and intellectual framework for describing and understanding all physical phenomena, except possibly for a quantum theory of gravity. Quantum Field Theory: A Modern Perspective presents Professor Nair’s view of certain topics in field theory loosely knit together as it gr...

  5. Quantum fields on manifolds: an interplay between quantum theory, statistical thermodynamics and general relativity

    International Nuclear Information System (INIS)

    Sewell, G.L.

    1986-01-01

    The author shows how the basic axioms of quantum field theory, general relativity and statistical thermodynamics lead, in a model-independent way, to a generalized Hawking-Unruh effect, whereby the gravitational fields carried by a class of space-time manifolds with event horizons thermalize ambient quantum fields. The author is concerned with a quantum field on a space-time x containing a submanifold X' bounded by event horizons. The objective is to show that, for a wide class of space-times, the global vacuum state of the field reduces, in X', to a thermal state, whose temperature depends on the geometry. The statistical thermodynaical, geometrical, and quantum field theoretical essential ingredients for the reduction of the vacuum state are discussed

  6. Theoretical Interpretation of Cosmic Magnetic Fields

    Science.gov (United States)

    Mikhail, F. I.; Wanas, M. I.; Eid, A. M.

    1995-06-01

    The paper discusses the possibilty of interpreting the magnetic fields of astronomical bodies in the framework of a unified field theory. Using one of the solutions of the generalized field theory, a direct relation between the polar magnetic field, the angular velocity and the gravitational potential of the body considered, is obtained. The geometric model used for applications has spherical symmetry and is of the type (FIGI). The predictions of the theoretical formula, obtained from the model, are compared with available observational data, and with the empirical formula of Blackett. The theoretical formula gives a possible interpretation of a seed magnetic field which will develop and produce the large-scale magnetic field observed for celestial objects. The formula shows that the field is generated as a result of rotation of a massive object.

  7. Quantum field theory in gravitational background

    International Nuclear Information System (INIS)

    Narnhofer, H.

    1986-01-01

    The author suggests ignoring the influence of the quantum field on the gravitation as the first step to combine quantum field theory and gravitation theory, but to consider the gravitational field as fixed and thus study quantum field theory on a manifold. This subject evoked interest when thermal radiation of a black hole was predicted. The author concentrates on the free quantum field and can split the problem into two steps: the Weyl-algebra of the free field and the Wightman functional on the tangent space

  8. Decoherence and dynamical entropy generation in quantum field theory

    Energy Technology Data Exchange (ETDEWEB)

    Koksma, Jurjen F., E-mail: J.F.Koksma@uu.nl [Institute for Theoretical Physics (ITP) and Spinoza Institute, Utrecht University, Postbus 80195, 3508 TD Utrecht (Netherlands); Prokopec, Tomislav, E-mail: T.Prokopec@uu.nl [Institute for Theoretical Physics (ITP) and Spinoza Institute, Utrecht University, Postbus 80195, 3508 TD Utrecht (Netherlands); Schmidt, Michael G., E-mail: M.G.Schmidt@thphys.uni-heidelberg.de [Institut fuer Theoretische Physik, Heidelberg University, Philosophenweg 16, D-69120 Heidelberg (Germany)

    2012-01-20

    We formulate a novel approach to decoherence based on neglecting observationally inaccessible correlators. We apply our formalism to a renormalised interacting quantum field theoretical model. Using out-of-equilibrium field theory techniques we show that the Gaussian von Neumann entropy for a pure quantum state increases to the interacting thermal entropy. This quantifies decoherence and thus measures how classical our pure state has become. The decoherence rate is equal to the single particle decay rate in our model. We also compare our approach to existing approaches to decoherence in a simple quantum mechanical model. We show that the entropy following from the perturbative master equation suffers from physically unacceptable secular growth.

  9. Analytic aspects of quantum fields

    CERN Document Server

    Bytsenko, A A; Elizalde, E; Moretti, V; Zerbini, S

    2003-01-01

    One of the aims of this book is to explain in a basic manner the seemingly difficult issues of mathematical structure using some specific examples as a guide. In each of the cases considered, a comprehensible physical problem is approached, to which the corresponding mathematical scheme is applied, its usefulness being duly demonstrated. The authors try to fill the gap that always exists between the physics of quantum field theories and the mathematical methods best suited for its formulation, which are increasingly demanding on the mathematical ability of the physicist. Contents: Survey of Pa

  10. Regularization of quantum field theories

    International Nuclear Information System (INIS)

    Rayski, J.

    1985-01-01

    General idea of regularization and renormalization in quantum field theory is presented. It is postulated that it is possible not to go to infinity with the auxiliary masses of regularization but to attach to them a certain physical meaning, but it is equivalent with a violation of unitarity of the operator of evolution in time. It may be achieved in two different ways: it might be simply assumed that only the direction but not the length of the state vector possesses a physical meaning and that not all possible physical events are predictable. 3 refs., 1 fig. (author)

  11. Lectures on classical and quantum theory of fields

    Energy Technology Data Exchange (ETDEWEB)

    Arodz, Henryk; Hadasz, Leszek [Jagiellonian Univ., Krakow (Poland). Inst. Physics

    2010-07-01

    This textbook on classical and quantum theory of fields addresses graduate students starting to specialize in theoretical physics. It provides didactic introductions to the main topics in the theory of fields, while taking into account the contemporary view of the subject. The student will find concise explanations of basic notions essential for applications of the theory of fields as well as for frontier research in theoretical physics. One third of the book is devoted to classical fields. Each chapter contains exercises of varying degree of difficulty with hints or solutions, plus summaries and worked examples as useful. The textbook is based on lectures delivered to students of theoretical physics at Jagiellonian University. It aims to deliver a unique combination of classical and quantum field theory in one compact course. (orig.)

  12. Towards quantum gravity via quantum field theory. Problems and perspectives

    Energy Technology Data Exchange (ETDEWEB)

    Fredenhagen, Klaus [II. Institut fuer Theoretische Physik, Universitaet Hamburg (Germany)

    2016-07-01

    General Relativity is a classical field theory; the standard methods for constructing a corresponding quantum field theory, however, meet severe difficulties, in particular perturbative non-renormalizability and the problem of background independence. Nevertheless, modern approaches to quantum field theory have significantly lowered these obstacles. On the side of non-renormalizability, this is the concept of effective theories, together with indications for better non-perturbative features of the renormalization group flow. On the side of background independence the main progress comes from an improved understanding of quantum field theories on generic curved spacetimes. Combining these informations, a promising approach to quantum gravity is an expansion around a classical solution which then is a quantum field theory on a given background, augmented by an identity which expresses independence against infinitesimal shifts of the background. The arising theory is expected to describe small corrections to classical general relativity. Inflationary cosmology is expected to arise as a lowest order approximation.

  13. Quantum field theory a tourist guide for mathematicians

    CERN Document Server

    Folland, Gerald B

    2008-01-01

    Quantum field theory has been a great success for physics, but it is difficult for mathematicians to learn because it is mathematically incomplete. Folland, who is a mathematician, has spent considerable time digesting the physical theory and sorting out the mathematical issues in it. Fortunately for mathematicians, Folland is a gifted expositor. The purpose of this book is to present the elements of quantum field theory, with the goal of understanding the behavior of elementary particles rather than building formal mathematical structures, in a form that will be comprehensible to mathematicians. Rigorous definitions and arguments are presented as far as they are available, but the text proceeds on a more informal level when necessary, with due care in identifying the difficulties. The book begins with a review of classical physics and quantum mechanics, then proceeds through the construction of free quantum fields to the perturbation-theoretic development of interacting field theory and renormalization theor...

  14. Quantum field theory lectures of Sidney Coleman

    CERN Document Server

    Derbes, David; Griffiths, David; Hill, Brian; Sohn, Richard; Ting, Yuan-Sen

    2018-01-01

    Sidney Coleman was a physicist's physicist. He is largely unknown outside of the theoretical physics community, and known only by reputation to the younger generation. He was an unusually effective teacher, famed for his wit, his insight and his encyclopedic knowledge of the field to which he made many important contributions. There are many first-rate quantum field theory books (the ancient Bjorken and Drell, the more modern Itzykson and Zuber, the now-standard Peskin and Schroder, and the recent Zee), but the immediacy of Prof. Coleman's approach and his ability to present an argument simply without sacrificing rigor makes his book easy to read and ideal for the student. Part of the motivation in producing this book is to pass on the work of this outstanding physicist to later generations, a record of his teaching that he was too busy to leave himself.

  15. Basic course theoretical physics. Vol. 5/1. Quantum mechanics - foundations. 7. upd. ed.

    International Nuclear Information System (INIS)

    Nolting, Wolfgang

    2009-01-01

    The favoured basic course theoretical physics covers in seven volumes all fields relevant for the diploma. Each volume mediates well thought the in each semester necessary theoretically-physical tools. Numerous exercise problem with extensive solutions serve for the deepening of the matter. The first part of the fifth volume begins with an inductive foundation of quantum mechanics in order to illustrate after a study and summary of the formal foundations of quantum mechanics on simple model systems the concepts and term formations. The present new edition was fundamentally worked out and supplemented. The meanwhile proved two-color presentation allows a very understandable and fast approach to the matter [de

  16. Theoretical Proposals of Quantum Phase-slip Devices

    NARCIS (Netherlands)

    Hriscu, A.M.

    2012-01-01

    This thesis describes a series of theoretical proposals of novel circuits that embed ultrathin superconducting nanowires with coherent quantum phase-slips (QPS). The motivation for our proposals is twofold: firstly, to facilitate unambiguous experimental verification of coherent phase-slips.

  17. The Quantum Cheshire Cat effect: Theoretical basis and observational implications

    Science.gov (United States)

    Duprey, Q.; Kanjilal, S.; Sinha, U.; Home, D.; Matzkin, A.

    2018-04-01

    The Quantum Cheshire Cat (QCC) is an effect introduced recently within the Weak Measurements framework. The main feature of the QCC effect is that a property of a quantum particle appears to be spatially separated from its position. The status of this effect has however remained unclear, as claims of experimental observation of the QCC have been disputed by strong criticism of the experimental as well as the theoretical aspects of the effect. In this paper we clarify in what precise sense the QCC can be regarded as an unambiguous consequence of the standard quantum mechanical formalism applied to describe quantum pointers weakly coupled to a system. In light of this clarification, the raised criticisms of the QCC effect are rebutted. We further point out that the limitations of the experiments performed to date imply that a loophole-free experimental demonstration of the QCC has not yet been achieved.

  18. On the embedding of quantum field theory on curved spacetimes into loop quantum gravity

    International Nuclear Information System (INIS)

    Stottmeister, Alexander

    2015-01-01

    The main theme of this thesis is an investigation into possible connections between loop quantum gravity and quantum field theory on curved spacetimes: On the one hand, we aim for the formulation of a general framework that allows for a derivation of quantum field theory on curved spacetimes in a semi-classical limit. On the other hand, we discuss representation-theoretical aspects of loop quantum gravity and quantum field theory on curved spacetimes as both of the latter presumably influence each other in the aforesaid semi-classical limit. Regarding the first point, we investigate the possible implementation of the Born-Oppenheimer approximation in the sense of space-adiabatic perturbation theory in models of loop quantum gravity-type. In the course of this, we argue for the need of a Weyl quantisation and an associated symbolic calculus for loop quantum gravity, which we then successfully define, at least to a certain extent. The compactness of the Lie groups, which models a la loop quantum gravity are based on, turns out to be a main obstacle to a fully satisfactory definition of a Weyl quantisation. Finally, we apply our findings to some toy models of linear scalar quantum fields on quantum cosmological spacetimes and discuss the implementation of space-adiabatic perturbation theory therein. In view of the second point, we start with a discussion of the microlocal spectrum condition for quantum fields on curved spacetimes and how it might be translated to a background-independent Hamiltonian quantum theory of gravity, like loop quantum gravity. The relevance of this lies in the fact that the microlocal spectrum condition selects a class of physically relevant states of the quantum matter fields and is, therefore, expected to play an important role in the aforesaid semi-classical limit of gravity-matter systems. Following this, we switch our perspective and analyse the representation theory of loop quantum gravity. We find some intriguing relations between the

  19. Quantum fields and processes a combinatorial approach

    CERN Document Server

    Gough, John

    2018-01-01

    Wick ordering of creation and annihilation operators is of fundamental importance for computing averages and correlations in quantum field theory and, by extension, in the Hudson–Parthasarathy theory of quantum stochastic processes, quantum mechanics, stochastic processes, and probability. This book develops the unified combinatorial framework behind these examples, starting with the simplest mathematically, and working up to the Fock space setting for quantum fields. Emphasizing ideas from combinatorics such as the role of lattice of partitions for multiple stochastic integrals by Wallstrom–Rota and combinatorial species by Joyal, it presents insights coming from quantum probability. It also introduces a 'field calculus' which acts as a succinct alternative to standard Feynman diagrams and formulates quantum field theory (cumulant moments, Dyson–Schwinger equation, tree expansions, 1-particle irreducibility) in this language. Featuring many worked examples, the book is aimed at mathematical physicists,...

  20. Lectures on classical and quantum theory of fields

    CERN Document Server

    Arodz, Henryk

    2017-01-01

    This textbook addresses graduate students starting to specialize in theoretical physics. It provides didactic introductions to the main topics in the theory of fields, while taking into account the contemporary view of the subject. The student will find concise explanations of basic notions essential for applications of the theory of fields as well as for frontier research in theoretical physics. One third of the book is devoted to classical fields. Each chapter contains exercises of varying degree of difficulty with hints or solutions, plus summaries and worked examples as useful. It aims to deliver a unique combination of classical and quantum field theory in one compact course.

  1. Particles, fields and quantum theory

    International Nuclear Information System (INIS)

    Bongaarts, P.J.M.

    1982-01-01

    The author gives an introduction to the development of gauge theories of the fundamental interactions. Starting from classical mechanics and quantum mechanics the development of quantum electrodynamics and non-abelian gauge theories is described. (HSI)

  2. An invitation to quantum field theory

    International Nuclear Information System (INIS)

    Alvarez-Gaume, Luis; Vazquez-Mozo, Miguel A.

    2012-01-01

    This book provides an introduction to Quantum Field Theory (QFT) at an elementary level - with only special relativity, electromagnetism and quantum mechanics as prerequisites. For this fresh approach to teaching QFT, based on numerous lectures and courses given by the authors, a representative sample of topics has been selected containing some of the more innovative, challenging or subtle concepts. They are presented with a minimum of technical details, the discussion of the main ideas being more important than the presentation of the typically very technical mathematical details necessary to obtain the final results. Special attention is given to the realization of symmetries in particle physics: global and local symmetries, explicit, spontaneously broken, and anomalous continuous symmetries, as well as discrete symmetries. Beyond providing an overview of the standard model of the strong, weak and electromagnetic interactions and the current understanding of the origin of mass, the text enumerates the general features of renormalization theory as well as providing a cursory description of effective field theories and the problem of naturalness in physics. Among the more advanced topics the reader will find are an outline of the first principles derivation of the CPT theorem and the spin-statistics connection. As indicated by the title, the main aim of this text is to motivate the reader to study QFT by providing a self-contained and approachable introduction to the most exciting and challenging aspects of this successful theoretical framework. (orig.)

  3. An invitation to quantum field theory

    Energy Technology Data Exchange (ETDEWEB)

    Alvarez-Gaume, Luis [CERN, Geneva (Switzerland). Physics Dept.; Vazquez-Mozo, Miguel A. [Salamanca Univ. (Spain). Dept. de Fisica Fundamental

    2012-07-01

    This book provides an introduction to Quantum Field Theory (QFT) at an elementary level - with only special relativity, electromagnetism and quantum mechanics as prerequisites. For this fresh approach to teaching QFT, based on numerous lectures and courses given by the authors, a representative sample of topics has been selected containing some of the more innovative, challenging or subtle concepts. They are presented with a minimum of technical details, the discussion of the main ideas being more important than the presentation of the typically very technical mathematical details necessary to obtain the final results. Special attention is given to the realization of symmetries in particle physics: global and local symmetries, explicit, spontaneously broken, and anomalous continuous symmetries, as well as discrete symmetries. Beyond providing an overview of the standard model of the strong, weak and electromagnetic interactions and the current understanding of the origin of mass, the text enumerates the general features of renormalization theory as well as providing a cursory description of effective field theories and the problem of naturalness in physics. Among the more advanced topics the reader will find are an outline of the first principles derivation of the CPT theorem and the spin-statistics connection. As indicated by the title, the main aim of this text is to motivate the reader to study QFT by providing a self-contained and approachable introduction to the most exciting and challenging aspects of this successful theoretical framework. (orig.)

  4. From quantum fields to fractal structures: intermittency in particle physics

    International Nuclear Information System (INIS)

    Peschanski, R.

    1991-01-01

    Some features and theoretical interpretations of the intermittency phenomenon observed in high-energy multi-particle production are recalled. One develops on the various connections found with fractal structuration of fluctuations in turbulence, spin-glass physics and aggregation phenomena described by the non-linear Smoluchowski equation. This may lead to a new approach to quantum field properties

  5. Analytic methods for field induced tunneling in quantum wells with ...

    Indian Academy of Sciences (India)

    Quantum wells (QW) formed in the semiconductor heterostructures have been given con- siderable theoretical attention because of their optical device applications [1]. For under- standing the operating principles of devices, it is necessary to study the optical absorption spectra in the QW under an applied dc electric field ...

  6. Relativistic quantum mechanics of leptons and fields

    International Nuclear Information System (INIS)

    Grandy, W.T. Jr.

    1991-01-01

    This book serves as an advanced text on the Dirac theory, and provides a monograph summarizing the description of relativistic quantum mechanics and quantum electrodynamics as classical field theories. It presents a broad, detailed, and up-to-date exposition of relativistic quantum mechanics, including the two-body problem. It also demonstrates the extent to which the behavior of stable particles and their interactions can be understood without introducing operator (second-quantized) fields. The subsequent difficulties are studied in detail and possible resolutions are presented through quantum field theory

  7. Relativistic quantum mechanics and field theory

    CERN Document Server

    Gross, Franz

    1999-01-01

    An accessible, comprehensive reference to modern quantum mechanics and field theory.In surveying available books on advanced quantum mechanics and field theory, Franz Gross determined that while established books were outdated, newer titles tended to focus on recent developments and disregard the basics. Relativistic Quantum Mechanics and Field Theory fills this striking gap in the field. With a strong emphasis on applications to practical problems as well as calculations, Dr. Gross provides complete, up-to-date coverage of both elementary and advanced topics essential for a well-rounded understanding of the field.

  8. Field-theoretical space-uncertainty description

    International Nuclear Information System (INIS)

    Papp, E.; Micu, C.A.

    1980-01-01

    An approach has been given to define both the nonzero minimum value of the space-uncertainty evaluation and of the upper rest-mass bound of the involved particles. In this respect there are analysed the space-uncertainties wich emerge both from the regularised quantum field-theory and high-energy behaviour. In such conditions there are involved particles wich are effectively nonpoint ones. It can be then concluded that the dualism broglien between waves and nonpoint particles is actually involved, now in more general terms

  9. A short course in quantum information theory. An approach from theoretical physics. 2. ed.

    International Nuclear Information System (INIS)

    Diosi, Lajos

    2011-01-01

    This short and concise primer takes the vantage point of theoretical physics and the unity of physics. It sets out to strip the burgeoning field of quantum information science to its basics by linking it to universal concepts in physics. An extensive lecture rather than a comprehensive textbook, this volume is based on courses delivered over several years to advanced undergraduate and beginning graduate students, but essentially it addresses anyone with a working knowledge of basic quantum physics. Readers will find these lectures a most adequate entry point for theoretical studies in this field. For the second edition, the authors has succeeded in adding many new topics while sticking to the conciseness of the overall approach. A new chapter on qubit thermodynamics has been added, while new sections and subsections have been incorporated in various chapter to deal with weak and time-continuous measurements, period-finding quantum algorithms and quantum error corrections. From the reviews of the first edition: ''The best things about this book are its brevity and clarity. In around 100 pages it provides a tutorial introduction to quantum information theory, including problems and solutions.. it's worth a look if you want to quickly get up to speed with the language and central concepts of quantum information theory, including the background classical information theory.'' (Craig Savage, Australian Physics, Vol. 44 (2), 2007). (orig.)

  10. Exact integrability in quantum field theory

    International Nuclear Information System (INIS)

    Thacker, H.B.

    1980-08-01

    The treatment of exactly integrable systems in various branches of two-dimensional classical and quantum physics has recently been placed in a unified framework by the development of the quantum inverse method. This method consolidates a broad range of developments in classical nonlinear wave (soliton) physics, statistical mechanics, and quantum field theory. The essential technique for analyzing exactly integrable quantum systems was invested by Bethe in 1931. The quantum-mechanical extension of the inverse scattering method and its relationship to the methods associated with Bethe's ansatz are examined here

  11. Proceedings of the international colloquium on modern quantum field theory II

    International Nuclear Information System (INIS)

    Das, S.R.; Mandal, G.; Mukhi, S.; Wadia, S.R.

    1995-01-01

    In the second International Colloquium on Modern Quantum Field Theory an attempt was made to cover a broad spectrum of topics in theoretical physics that included string theory, quantum gravity, statistical mechanics, condensed matter theory, complexity, lattice gauge theory and epistemological aspects of quantum mechanics. Papers relevant to INIS in the published proceedings are indexed separately

  12. Theoretical physics 7 quantum mechanics : methods and applications

    CERN Document Server

    Nolting, Wolfgang

    2017-01-01

    This textbook offers a clear and comprehensive introduction to methods and applications in quantum mechanics, one of the core components of undergraduate physics courses. It follows on naturally from the previous volumes in this series, thus developing the understanding of quantized states further on. The first part of the book introduces the quantum theory of angular momentum and approximation methods. More complex themes are covered in the second part of the book, which describes multiple particle systems and scattering theory. Ideally suited to undergraduate students with some grounding in the basics of quantum mechanics, the book is enhanced throughout with learning features such as boxed inserts and chapter summaries, with key mathematical derivations highlighted to aid understanding. The text is supported by numerous worked examples and end of chapter problem sets.  About the Theoretical Physics series Translated from the renowned and highly successful German editions, the eight volumes of this seri...

  13. Dark Matter, Elko Fields and Weinberg's Quantum Field Theory Formalism

    Science.gov (United States)

    Gillard, Adam; Martin, Benjamin

    2012-02-01

    The Elko quantum field was introduced by Ahluwalia and Grumiller, who proposed it as a candidate for dark matter. We study the Elko field in Wemberg's formalism for quantum field theory. We prove that if one takes the symmetry group to be the full Pomcaré group then the Elko field is not a quantum field in the sense of Weinberg. This confirms results of Ahluwalia, Lee and Schritt, who showed using a different approach that the Elko field does not transform covariantly under rotations and hence has a preferred axis.

  14. A field theoretic model for static friction

    OpenAIRE

    Mahyaeh, I.; Rouhani, S.

    2013-01-01

    We present a field theoretic model for friction, where the friction coefficient between two surfaces may be calculated based on elastic properties of the surfaces. We assume that the geometry of contact surface is not unusual. We verify Amonton's laws to hold that friction force is proportional to the normal load.This model gives the opportunity to calculate the static coefficient of friction for a few cases, and show that it is in agreement with observed values. Furthermore we show that the ...

  15. Quantum mechanics. Textbook on theoretical physics III. 4. rev. ed.

    International Nuclear Information System (INIS)

    Fliessbach, T.

    2005-01-01

    This textbook present an intoduction to quantum mechanics, as it is offerred at the university in the cycle ''Theoretical Physics''. Special value has the author put on a well readable, understandable, and surveyable representation, so that the reader it can reproduce without larger difficulties. By the partition into chapters, which form separated course units, and the kind of the representation the book is also suited for bachelor curricula. The quantum mechanics are first introduced in the form of Schroedinge's wave mechanics. The fundamental relations of quantum mechanics and their interpretation are thereby explained by means of examples and first applications. In the following chapters the most important applications of the Schroedinger equation are studied, like the alpha decay, the scattering of a particle on a potential, and the hydrogen atom. Thereafter the abstract formulation of quantum mechanics (Hilbert space) is introduced in analogy to the known structure of the vector space. This formulation is then applied to concrete problems like the oscillator, tha angular momentum, and the spin. The most important approximation methods of quantum mechanics are then summarized. In the concluding part about many-particle systems the ideal Fermi gas is treated; simple applications of this model in atomic, solid-state, nuclear, ans astrophysics are discussed

  16. Mathematical aspects of quantum field theory

    CERN Document Server

    de Faria, Edson

    2010-01-01

    Over the last century quantum field theory has made a significant impact on the formulation and solution of mathematical problems and inspired powerful advances in pure mathematics. However, most accounts are written by physicists, and mathematicians struggle to find clear definitions and statements of the concepts involved. This graduate-level introduction presents the basic ideas and tools from quantum field theory to a mathematical audience. Topics include classical and quantum mechanics, classical field theory, quantization of classical fields, perturbative quantum field theory, renormalization, and the standard model. The material is also accessible to physicists seeking a better understanding of the mathematical background, providing the necessary tools from differential geometry on such topics as connections and gauge fields, vector and spinor bundles, symmetries and group representations.

  17. Theoretical discussion for quantum computation in biological systems

    Science.gov (United States)

    Baer, Wolfgang

    2010-04-01

    Analysis of the brain as a physical system, that has the capacity of generating a display of every day observed experiences and contains some knowledge of the physical reality which stimulates those experiences, suggests the brain executes a self-measurement process described by quantum theory. Assuming physical reality is a universe of interacting self-measurement loops, we present a model of space as a field of cells executing such self-measurement activities. Empty space is the observable associated with the measurement of this field when the mass and charge density defining the material aspect of the cells satisfy the least action principle. Content is the observable associated with the measurement of the quantum wave function ψ interpreted as mass-charge displacements. The illusion of space and its content incorporated into cognitive biological systems is evidence of self-measurement activity that can be associated with quantum operations.

  18. Linking topological quantum field theory and nonperturbative quantum gravity

    Science.gov (United States)

    Smolin, Lee

    1995-11-01

    Quantum gravity is studied nonperturbatively in the case in which space has a boundary with finite area. A natural set of boundary conditions is studied in the Euclidean signature theory in which the pullback of the curvature to the boundary is self-dual (with a cosmological constant). A Hilbert space which describes all the information accessible by measuring the metric and connection induced in the boundary is constructed and is found to be the direct sum of the state spaces of all SU(2) Chern-Simon theories defined by all choices of punctures and representations on the spatial boundary S. The integer level k of Chern-Simons theory is found to be given by k=6π/G2Λ+α, where Λ is the cosmological constant and α is a CP breaking phase. Using these results, expectation values of observables which are functions of fields on the boundary may be evaluated in closed form. Given these results, it is natural to make the conjecture that the quantum states of the system are completely determined by measurements made on the boundary. One consequence of this is the Bekenstein bound, which says that once the two metric of the boundary has been measured, the subspace of the physical state space that describes the further information that may be obtained about the interior has finite dimension equal to the exponent of the area of the boundary, in Planck units, times a fixed constant. Finally, these results confirm both the categorical-theoretic ``ladder of dimensions'' picture of Crane and the holographic hypothesis of Susskind and 't Hooft.

  19. Neutrix calculus and finite quantum field theory

    International Nuclear Information System (INIS)

    Ng, Y Jack; Dam, H van

    2005-01-01

    In general, quantum field theories (QFT) require regularizations and infinite renormalizations due to ultraviolet divergences in their loop calculations. Furthermore, perturbation series in theories like quantum electrodynamics are not convergent series, but are asymptotic series. We apply neutrix calculus, developed in connection with asymptotic series and divergent integrals, to QFT, obtaining finite renormalizations. While none of the physically measurable results in renormalizable QFT is changed, quantum gravity is rendered more manageable in the neutrix framework. (letter to the editor)

  20. Classical field approach to quantum weak measurements.

    Science.gov (United States)

    Dressel, Justin; Bliokh, Konstantin Y; Nori, Franco

    2014-03-21

    By generalizing the quantum weak measurement protocol to the case of quantum fields, we show that weak measurements probe an effective classical background field that describes the average field configuration in the spacetime region between pre- and postselection boundary conditions. The classical field is itself a weak value of the corresponding quantum field operator and satisfies equations of motion that extremize an effective action. Weak measurements perturb this effective action, producing measurable changes to the classical field dynamics. As such, weakly measured effects always correspond to an effective classical field. This general result explains why these effects appear to be robust for pre- and postselected ensembles, and why they can also be measured using classical field techniques that are not weak for individual excitations of the field.

  1. A new way of visualising quantum fields

    Science.gov (United States)

    Linde, Helmut

    2018-05-01

    Quantum field theory (QFT) is the basis of some of the most fundamental theories in modern physics, but it is not an easy subject to learn. In the present article we intend to pave the way from quantum mechanics to QFT for students at early graduate or advanced undergraduate level. More specifically, we propose a new way of visualising the wave function Ψ of a linear chain of interacting quantum harmonic oscillators, which can be seen as a model for a simple one-dimensional bosonic quantum field. The main idea is to draw randomly chosen classical states of the chain superimposed upon each other and use a grey scale to represent the value of Ψ at the corresponding coordinates of the quantised system. Our goal is to establish a better intuitive understanding of the mathematical objects underlying quantum field theories and solid state physics.

  2. Circuit complexity in quantum field theory

    Science.gov (United States)

    Jefferson, Robert A.; Myers, Robert C.

    2017-10-01

    Motivated by recent studies of holographic complexity, we examine the question of circuit complexity in quantum field theory. We provide a quantum circuit model for the preparation of Gaussian states, in particular the ground state, in a free scalar field theory for general dimensions. Applying the geometric approach of Nielsen to this quantum circuit model, the complexity of the state becomes the length of the shortest geodesic in the space of circuits. We compare the complexity of the ground state of the free scalar field to the analogous results from holographic complexity, and find some surprising similarities.

  3. Optical graphene quantum dots gas sensors: Theoretical study

    Science.gov (United States)

    Raeyani, D.; Shojaei, S.; Ahmadi-Kandjani, S.

    2018-02-01

    In this work, we theoretically studied the changes of graphene quantum dots (GQD) absorption spectra under the influence of different gases to indicate optical gas sensing features of GQDs. The adsorption of gas molecules such as CO2, N2 and Ar on GQDs have been theoretically investigated through time-dependent density functional theory (TDDFT) calculations. Our study revealed that UV-Vis absorption spectrum of GQDs in the presence of CO2 undergoes considerable changes than that of N2 and Ar. The shift of maximum absorption wavelength for adsorption of CO2, N2 and Ar in same distance from GQD in addition to density of state (DOS) and orbital analyses have been obtained. To verify our theoretical results, comparison with experimental study has been done and good agreement has been observed. Comparing with electrical property of GQD, optical properties showed an efficient tool to be implemented in gas adsorption and paves the way towards GQD optical gas sensors.

  4. Quantum Field Theory in a Semiotic Perspective

    CERN Document Server

    Günter Dosch, Hans; Sieroka, Norman

    2005-01-01

    Viewing physical theories as symbolic constructions came to the fore in the middle of the nineteenth century with the emancipation of the classical theory of the electromagnetic field from mechanics; most notably this happened through the work of Helmholtz, Hertz, Poincaré, and later Weyl. The epistemological problems that nourished this development are today highlighted within quantum field theory. The present essay starts off with a concise and non-technical outline of the firmly based aspects of relativistic quantum field theory, i.e. the very successful description of subnuclear phenomena. The particular methods, by which these different aspects have to be accessed, then get described as distinct facets of quantum field theory. The authors show how these different facets vary with respect to the relation between quantum fields and associated particles. Thus, by emphasising the respective role of various basic concepts involved, the authors claim that only a very general epistemic approach can properly ac...

  5. The conceptual basis of Quantum Field Theory

    NARCIS (Netherlands)

    Hooft, G. 't

    2005-01-01

    Relativistic Quantum Field Theory is a mathematical scheme to describe the sub-atomic particles and forces. The basic starting point is that the axioms of Special Relativity on the one hand and those of Quantum Mechanics on the other, should be combined into one theory. The fundamental

  6. The quantum symmetry of rational field theories

    International Nuclear Information System (INIS)

    Fuchs, J.

    1993-12-01

    The quantum symmetry of a rational quantum field theory is a finite-dimensional multi-matrix algebra. Its representation category, which determines the fusion rules and braid group representations of superselection sectors, is a braided monoidal C*-category. Various properties of such algebraic structures are described, and some ideas concerning the classification programme are outlined. (orig.)

  7. Mathematical methods of many-body quantum field theory

    CERN Document Server

    Lehmann, Detlef

    2004-01-01

    Mathematical Methods of Many-Body Quantum Field Theory offers a comprehensive, mathematically rigorous treatment of many-body physics. It develops the mathematical tools for describing quantum many-body systems and applies them to the many-electron system. These tools include the formalism of second quantization, field theoretical perturbation theory, functional integral methods, bosonic and fermionic, and estimation and summation techniques for Feynman diagrams. Among the physical effects discussed in this context are BCS superconductivity, s-wave and higher l-wave, and the fractional quantum Hall effect. While the presentation is mathematically rigorous, the author does not focus solely on precise definitions and proofs, but also shows how to actually perform the computations.Presenting many recent advances and clarifying difficult concepts, this book provides the background, results, and detail needed to further explore the issue of when the standard approximation schemes in this field actually work and wh...

  8. Rigorous Quantum Field Theory A Festschrift for Jacques Bros

    CERN Document Server

    Monvel, Anne Boutet; Iagolnitzer, Daniel; Moschella, Ugo

    2007-01-01

    Jacques Bros has greatly advanced our present understanding of rigorous quantum field theory through numerous fundamental contributions. This book arose from an international symposium held in honour of Jacques Bros on the occasion of his 70th birthday, at the Department of Theoretical Physics of the CEA in Saclay, France. The impact of the work of Jacques Bros is evident in several articles in this book. Quantum fields are regarded as genuine mathematical objects, whose various properties and relevant physical interpretations must be studied in a well-defined mathematical framework. The key topics in this volume include analytic structures of Quantum Field Theory (QFT), renormalization group methods, gauge QFT, stability properties and extension of the axiomatic framework, QFT on models of curved spacetimes, QFT on noncommutative Minkowski spacetime. Contributors: D. Bahns, M. Bertola, R. Brunetti, D. Buchholz, A. Connes, F. Corbetta, S. Doplicher, M. Dubois-Violette, M. Dütsch, H. Epstein, C.J. Fewster, K....

  9. Quantum mechanics. Textbook on Theoretical Physics III. 5. ed.

    International Nuclear Information System (INIS)

    Fliessbach, Torsten

    2008-01-01

    This textbook gives an introduction to quantum mechanics, as it is presented at the university in the cycle ''Theoretical Physics''. Special care has the author put om a well readable, understandable, and clearly arranged presentation, so that the reader can it reproduce without greater difficulties. By the partition into chapters, which form self-contained teaching units, and the kind of presentation the book is also very well suited for bachelor courses. Quantum mechanics is first introduced in form of Schroedinger's wave mechanics. The fundamental relations and their interpretation are thereby explained hand in hand with examples and first applications. In the following parts the most important applications of the Schroedinger equation are studied, as the alpha decay, the scattering of particles on a potential, and the hydrogen atom. Thereafter the abstract formulation of quantum mechanics (Hilbert space) is introduced in analogy to the known structure of the vector space. This formulation is applied to concrete problems, as the oscillator, the angular momentum, and the spin. The most important approximation methods of quantum mechanics are then summarized. In the final part about many-particle systems the ideal Fermi gas is treated; simple application of this model in atomic, solid-state,and astrophysics are discussed

  10. An introduction to relativistic quantum field theory

    CERN Document Server

    Schweber, Silvan S

    1961-01-01

    Complete, systematic, and self-contained, this text introduces modern quantum field theory. "Combines thorough knowledge with a high degree of didactic ability and a delightful style." - Mathematical Reviews. 1961 edition.

  11. Ab-initio Hamiltonian approach to light nuclei and to quantum field ...

    Indian Academy of Sciences (India)

    A successful microscopic non-perturbative Hamiltonian approach to low-energy ... We illustrate key ingredients of the theoretical frameworks .... factor of 2. 4. Approach to quantum field theory. Hamiltonian light-front quantum field theory has a long history [9]. Our approach is to establish a convenient basis space expansion ...

  12. Maxwell's demon. (II) A quantum-theoretic exorcism

    Science.gov (United States)

    Gyftopoulos, Elias P.

    2002-05-01

    In Part II of this two-part paper we prove that Maxwell's demon is unable to accomplish his task of sorting air molecules into swift and slow because in air in a thermodynamic equilibrium state there are no such molecules. The proof is based on the principles of a unified quantum theory of mechanics and thermodynamics. The key idea of the unified theory is that von Neumann's concept of a homogeneous ensemble of identical systems, identically prepared, is valid not only for a density operator ρ equal to a projector (every member of the ensemble is assigned the same projector, ρi=| ψi> ρ 2, as any other member). So, the latter ensemble is not a statistical mixture of projectors. The broadening of the validity of the homogeneous ensemble is consistent with the quantum-theoretic postulates about observables, measurement results, and value of any observable. In the context of the unified theory, among the many novel results is the theorem that each molecule of a system in a thermodynamic equilibrium state has zero value of momentum, that is, each molecule is at a standstill and, therefore, there are no molecules to be sorted as swift and slow. Said differently, if Maxwell were cognizant of quantum theory, he would not have conceived of the idea of the demon. It is noteworthy that the zero value of momentum is not the result of averaging over different momenta of many molecules. Under the specified conditions, it is the quantum-theoretic value of the momentum of any one molecule, and the same result is valid even if the system consists of only one molecule.

  13. Mathematical aspects of quantum field theories

    CERN Document Server

    Strobl, Thomas

    2015-01-01

    Despite its long history and stunning experimental successes, the mathematical foundation of perturbative quantum field theory is still a subject of ongoing research. This book aims at presenting some of the most recent advances in the field, and at reflecting the diversity of approaches and tools invented and currently employed. Both leading experts and comparative newcomers to the field present their latest findings, helping readers to gain a better understanding of not only quantum but also classical field theories. Though the book offers a valuable resource for mathematicians and physicists alike, the focus is more on mathematical developments. This volume consists of four parts: The first Part covers local aspects of perturbative quantum field theory, with an emphasis on the axiomatization of the algebra behind the operator product expansion. The second Part highlights Chern-Simons gauge theories, while the third examines (semi-)classical field theories. In closing, Part 4 addresses factorization homolo...

  14. Wedge-local quantum fields and interaction

    International Nuclear Information System (INIS)

    Lechner, G.

    2007-01-01

    In the construction of relativistic quantum field theories, field operators which are not point-localized, but rather localized in wedge-shaped regions of d-dimensional Minkowski space, are a novel tool. We present a family of concrete examples of such wedge-local quantum fields in 4-dimensional spacetime by making use of a correspondence between wedges and noncommutativity parameters. It is then discussed to which degree models formulated in terms of wedge-local fields comply with the principle of locality. One of our examples is closely related to the free field on non-commutative Minkowski space, which can also be understood as a wedge-local quantum field. (author)

  15. Quantum field theory the why, what and how

    CERN Document Server

    Padmanabhan, Thanu

    2016-01-01

    This book describes, in clear terms, the Why, What and the How of Quantum Field Theory. The raison d'etre of QFT is explained by starting from the dynamics of a relativistic particle and demonstrating how it leads to the notion of quantum fields. Non-perturbative aspects and the Wilsonian interpretation of field theory are emphasized right from the start. Several interesting topics such as the Schwinger effect, Davies-Unruh effect, Casimir effect and spontaneous symmetry breaking introduce the reader to the elegance and breadth of applicability of field theoretical concepts. Complementing the conceptual aspects, the book also develops all the relevant mathematical techniques in detail, leading e.g., to the computation of anomalous magnetic moment of the electron and the two-loop renormalisation of the self-interacting scalar field. It contains nearly a hundred problems, of varying degrees of difficulty, making it suitable for both self-study and classroom use.

  16. Introduction to classical and quantum field theory

    International Nuclear Information System (INIS)

    Ng, Tai-Kai

    2009-01-01

    This is the first introductory textbook on quantum field theory to be written from the point of view of condensed matter physics. As such, it presents the basic concepts and techniques of statistical field theory, clearly explaining how and why they are integrated into modern quantum (and classical) field theory, and includes the latest developments. Written by an expert in the field, with a broad experience in teaching and training, it manages to present such substantial topics as phases and phase transitions or solitons and instantons in an accessible and concise way. Divided into three parts, the first part covers fundamental physics and the mathematics background needed by students in order to enter the field, while the second part introduces more advanced concepts and techniques. Part III discusses applications of quantum field theory to a few basic problems. The emphasis here lies on how modern concepts of quantum field theory are embedded in these approaches, and also on the limitations of standard quantum field theory techniques in facing, 'real' physics problems. Throughout there are numerous end-of-chapter problems, and a free solutions manual is available for lecturers. (orig.)

  17. Zero field spin splitting in asymmetric quantum wells

    International Nuclear Information System (INIS)

    Hao Yafei

    2012-01-01

    Spin splitting of asymmetric quantum wells is theoretically investigated in the absence of any electric field, including the contribution of interface-related Rashba spin-orbit interaction as well as linear and cubic Dresselhaus spin-orbit interaction. The effect of interface asymmetry on three types of spin-orbit interaction is discussed. The results show that interface-related Rashba and linear Dresselhaus spin-orbit interaction can be increased and cubic Dresselhaus spin-orbit interaction can be decreased by well structure design. For wide quantum wells, the cubic Dresselhaus spin-orbit interaction dominates under certain conditions, resulting in decreased spin relaxation time.

  18. The conceptual framework of quantum field theory

    CERN Document Server

    Duncan, Anthony

    2012-01-01

    The book attempts to provide an introduction to quantum field theory emphasizing conceptual issues frequently neglected in more "utilitarian" treatments of the subject. The book is divided into four parts, entitled respectively "Origins", "Dynamics", "Symmetries", and "Scales". The emphasis is conceptual - the aim is to build the theory up systematically from some clearly stated foundational concepts - and therefore to a large extent anti-historical, but two historical Chapters ("Origins") are included to situate quantum field theory in the larger context of modern physical theories. The three remaining sections of the book follow a step by step reconstruction of this framework beginning with just a few basic assumptions: relativistic invariance, the basic principles of quantum mechanics, and the prohibition of physical action at a distance embodied in the clustering principle. The "Dynamics" section of the book lays out the basic structure of quantum field theory arising from the sequential insertion of quan...

  19. Role of information theoretic uncertainty relations in quantum theory

    International Nuclear Information System (INIS)

    Jizba, Petr; Dunningham, Jacob A.; Joo, Jaewoo

    2015-01-01

    Uncertainty relations based on information theory for both discrete and continuous distribution functions are briefly reviewed. We extend these results to account for (differential) Rényi entropy and its related entropy power. This allows us to find a new class of information-theoretic uncertainty relations (ITURs). The potency of such uncertainty relations in quantum mechanics is illustrated with a simple two-energy-level model where they outperform both the usual Robertson–Schrödinger uncertainty relation and Shannon entropy based uncertainty relation. In the continuous case the ensuing entropy power uncertainty relations are discussed in the context of heavy tailed wave functions and Schrödinger cat states. Again, improvement over both the Robertson–Schrödinger uncertainty principle and Shannon ITUR is demonstrated in these cases. Further salient issues such as the proof of a generalized entropy power inequality and a geometric picture of information-theoretic uncertainty relations are also discussed

  20. Basic course theoretical physics 5/2. Quantum mechanics - methods and applications. 7. upd. ed.

    International Nuclear Information System (INIS)

    Nolting, Wolfgang

    2012-01-01

    The favourite basic course theoretical physics covers in seven volumes all for the diploma and bachelor/master curricula decisive fields. Each volume mediates well considerably the theoretic-physical knowledge necessary in each semester. Numerous exercise problems with extended solutions serve for the deepening of the matter. The second part of the fifth volume deals with application and the extension of the concept of quantum mechanics developed in the first part. The present new edition contains some new problems, was worked out, and supplemented. It makes by the two-colour presentation a very distinct and fast access to the subject of teaching.

  1. Quantum processes: A Whiteheadian interpretation of quantum field theory

    Science.gov (United States)

    Bain, Jonathan

    Quantum processes: A Whiteheadian interpretation of quantum field theory is an ambitious and thought-provoking exercise in physics and metaphysics, combining an erudite study of the very complex metaphysics of A.N. Whitehead with a well-informed discussion of contemporary issues in the philosophy of algebraic quantum field theory. Hättich's overall goal is to construct an interpretation of quantum field theory. He does this by translating key concepts in Whitehead's metaphysics into the language of algebraic quantum field theory. In brief, this Hättich-Whitehead (H-W, hereafter) interpretation takes "actual occasions" as the fundamental ontological entities of quantum field theory. An actual occasion is the result of two types of processes: a "transition process" in which a set of initial possibly-possessed properties for the occasion (in the form of "eternal objects") is localized to a space-time region; and a "concrescence process" in which a subset of these initial possibly-possessed properties is selected and actualized to produce the occasion. Essential to these processes is the "underlying activity", which conditions the way in which properties are initially selected and subsequently actualized. In short, under the H-W interpretation of quantum field theory, an initial set of possibly-possessed eternal objects is represented by a Boolean sublattice of the lattice of projection operators determined by a von Neumann algebra R (O) associated with a region O of Minkowski space-time, and the underlying activity is represented by a state on R (O) obtained by conditionalizing off of the vacuum state. The details associated with the H-W interpretation involve imposing constraints on these representations motivated by principles found in Whitehead's metaphysics. These details are spelled out in the three sections of the book. The first section is a summary and critique of Whitehead's metaphysics, the second section introduces the formalism of algebraic quantum field

  2. Theoretical Study of Solid State Quantum Information Processing

    Science.gov (United States)

    2013-08-28

    Implementing a topological quantum model using a cavity lattice , Science China Physics, Mechanics and Astronomy, (07 2012): 0. doi: 10.1007/s11433... Rabi frequency as a function of the magnetic field for sufficiently large Zeeman energies, which can alternatively be interpreted as the magnetic...DQD), where coherent Rabi oscillations between the singlet and triplet states are induced by jittering the inter-dot distance at the resonance

  3. Bookshelf (The Quantum Theory of Fields, La lumiere des neutrinos)

    International Nuclear Information System (INIS)

    Anon.

    1995-01-01

    The Quantum Theory of Fields Volume 1: Foundations by Steven Weinberg, Cambridge University Press, 1995: Steven Weinberg is celebrated for his many contributions to quantum field theory and its applications to elementary particle physics - most notably, for developing the electroweak theory, the unified model of the electromagnetic and weak forces that forms part of the Standard Model that has explained essentially all accelerator data on the behaviour of elementary particles. This is the culmination of the developments in quantum field theory that started in the early days of quantum mechanics and came to maturity with the development of quantum electrodynamics in the late 1940s. Quantum field theory is the basic theoretical framework for research in particle physics as well as in many areas of condensed matter physics. No wonder the community has been waiting with anticipation for Weinberg's exposition of the subject in the form of a two-volume textbook - the more so since, despite the existence of many textbooks, few of them are written with the insight and detail that are needed for a thorough understanding. The community will not be disappointed, at least on the basis of this first volume - Volume 2 is due to appear next year. Volume 1 is 600 pages of meticulous exposition of the fundamentals of the subject, starting from a historical introduction and the canonical formulation of quantum field theory to modern path integral methods applied to the quantization of electrodynamics and a first discussion of renormaiization. In addition to a superb treatment of all the conventional topics there are numerous sections covering areas that are not normally emphasized, such as the subject of field redefinitions, higher-rank tensor fields and an unusually clear and thorough treatment of infrared effects. This is only the basics - Volume 2 promises to develop the subjects at the cutting edge of modern research such as Yang-Mills theory, the renormalization group

  4. Macroscopic Quantum-Type Potentials in Theoretical Systems Biology

    Directory of Open Access Journals (Sweden)

    Laurent Nottale

    2013-12-01

    Full Text Available We review in this paper the use of the theory of scale relativity and fractal space-time as a tool particularly well adapted to the possible development of a future genuine systems theoretical biology. We emphasize in particular the concept of quantum-type potentials, since, in many situations, the effect of the fractality of space—or of the underlying medium—can be reduced to the addition of such a potential energy to the classical equations of motion. Various equivalent representations—geodesic, quantum-like, fluid mechanical, stochastic—of these equations are given, as well as several forms of generalized quantum potentials. Examples of their possible intervention in high critical temperature superconductivity and in turbulence are also described, since some biological processes may be similar in some aspects to these physical phenomena. These potential extra energy contributions could have emerged in biology from the very fractal nature of the medium, or from an evolutive advantage, since they involve spontaneous properties of self-organization, morphogenesis, structuration and multi-scale integration. Finally, some examples of applications of the theory to actual biological-like processes and functions are also provided.

  5. Quantum field theory in a semiotic perspective

    International Nuclear Information System (INIS)

    Dosch, H.G.

    2005-01-01

    Viewing physical theories as symbolic constructions came to the fore in the middle of the nineteenth century with the emancipation of the classical theory of the electromagnetic field from mechanics; most notably this happened through the work of Helmholtz, Hertz, Poincare, and later Weyl. The epistemological problems that nourished this development are today highlighted within quantum field theory. The present essay starts off with a concise and non-technical outline of the firmly based aspects of relativistic quantum field theory, i.e. the very successful description of subnuclear phenomena. The particular methods, by which these different aspects have to be accessed, then get described as distinct facets of quantum field theory. The authors show how these different facets vary with respect to the relation between quantum fields and associated particles. Thus, by emphasising the respective role of various basic concepts involved, the authors claim that only a very general epistemic approach can properly account for this diversity - an account they trace back to the philosophical writings of the aforementioned physicists and mathematicians. Finally, what they call their semiotic perspective on quantum field theory gets related to recent discussions within the philosophy of science and turns out to act as a counterbalance to, for instance, structural realism. (orig.)

  6. Quantum field theory in a semiotic perspective

    Energy Technology Data Exchange (ETDEWEB)

    Dosch, H.G. [Heidelberg Univ. (Germany). Inst. fuer Theoretische Physik; Mueller, V.F. [Technische Univ. Kaiserslautern (Germany). Fachbereich Physik; Sieroka, N. [Zurich Univ. (Switzerland)

    2005-07-01

    Viewing physical theories as symbolic constructions came to the fore in the middle of the nineteenth century with the emancipation of the classical theory of the electromagnetic field from mechanics; most notably this happened through the work of Helmholtz, Hertz, Poincare, and later Weyl. The epistemological problems that nourished this development are today highlighted within quantum field theory. The present essay starts off with a concise and non-technical outline of the firmly based aspects of relativistic quantum field theory, i.e. the very successful description of subnuclear phenomena. The particular methods, by which these different aspects have to be accessed, then get described as distinct facets of quantum field theory. The authors show how these different facets vary with respect to the relation between quantum fields and associated particles. Thus, by emphasising the respective role of various basic concepts involved, the authors claim that only a very general epistemic approach can properly account for this diversity - an account they trace back to the philosophical writings of the aforementioned physicists and mathematicians. Finally, what they call their semiotic perspective on quantum field theory gets related to recent discussions within the philosophy of science and turns out to act as a counterbalance to, for instance, structural realism. (orig.)

  7. Quantum field theory in topology changing spacetimes

    International Nuclear Information System (INIS)

    Bauer, W.

    2007-03-01

    The goal of this diploma thesis is to present an overview of how to reduce the problem of topology change of general spacetimes to the investigation of elementary cobordisms. In the following we investigate the possibility to construct quantum fields on elementary cobordisms, in particular we discuss the trousers topology. Trying to avoid the problems occuring at spacetimes with instant topology change we use a model for simulating topology change. We construct the algebra of observables for a free scalar field with the algebraic approach to quantum field theory. Therefore we determine a fundamental solution of the eld equation. (orig.)

  8. Dynamical symmetry breaking in quantum field theories

    CERN Document Server

    Miransky, Vladimir A

    1993-01-01

    The phenomenon of dynamical symmetry breaking (DSB) in quantum field theory is discussed in a detailed and comprehensive way. The deep connection between this phenomenon in condensed matter physics and particle physics is emphasized. The realizations of DSB in such realistic theories as quantum chromodynamics and electroweak theory are considered. Issues intimately connected with DSB such as critical phenomenona and effective lagrangian approach are also discussed.

  9. A measure theoretical approach to quantum stochastic processes

    CERN Document Server

    Von Waldenfels, Wilhelm

    2014-01-01

    This monograph takes as starting point that abstract quantum stochastic processes can be understood as a quantum field theory in one space and in one time coordinate. As a result it is appropriate to represent operators as power series of creation and annihilation operators in normal-ordered form, which can be achieved using classical measure theory. Considering in detail four basic examples (e.g. a two-level atom coupled to a heat bath of oscillators), in each case the Hamiltonian of the associated one-parameter strongly continuous group is determined and the spectral decomposition is explicitly calculated in the form of generalized eigen-vectors. Advanced topics include the theory of the Hudson-Parthasarathy equation and the amplified oscillator problem. To that end, a chapter on white noise calculus has also been included.

  10. Constructions of quantum fields with anyonic statistics

    International Nuclear Information System (INIS)

    Plaschke, M.

    2015-01-01

    From the principles of algebraic quantum field theory it follows that in low dimensions particles are not necessarily bosons or fermions, but their statistics can in general be governed by the braid group. Such particles are called anyons and their possible statistics is intimately related to their localization properties and their covariance with respect to rotations. This work is concerned with the explicit construction of quantum fields with anyonic statistics which are localized in various different regions on two- and three-dimensional Minkowski space, and we will analyze the connection between localization, statistics and spin. The reason why this is considerably more difficult than for bosons or fermions is the no-go theorem regarding free cone-localized anyons in d=2+1. This problem is approached in this work from different directions leaving out some of the underlying assumptions one makes in the abstract algebraic quantum field theory. Despite a similar no-go theorem for free local anyons, it is in two dimensions possible to construct compactly localized quantum field nets with anyonic commutation relations for every mass m ≥ 0 and every statistics parameter by using the theory of loop groups and implementable Bogoliubov transformations. This does not work in higher dimensions so in d=2+1 we will first construct polarization free generators, which are only wedge-local, using a recent work about multiplicative deformations of free quantum fields on the Fock space. By generalizing this procedure to the charged case it is possible to extend the set of admissible deformations and end up with fields satisfying anyonic commutation relations, which are covariant w.r.t a Poincaré group representation with arbitrary real-valued spin. Another approach, which further demonstrates the connection between localization, statistics and spin of quantum field nets, is to focus first only on the rotational degrees of freedom and construct field operators on the circle

  11. Dual field theories of quantum computation

    International Nuclear Information System (INIS)

    Vanchurin, Vitaly

    2016-01-01

    Given two quantum states of N q-bits we are interested to find the shortest quantum circuit consisting of only one- and two- q-bit gates that would transfer one state into another. We call it the quantum maze problem for the reasons described in the paper. We argue that in a large N limit the quantum maze problem is equivalent to the problem of finding a semiclassical trajectory of some lattice field theory (the dual theory) on an N+1 dimensional space-time with geometrically flat, but topologically compact spatial slices. The spatial fundamental domain is an N dimensional hyper-rhombohedron, and the temporal direction describes transitions from an arbitrary initial state to an arbitrary target state and so the initial and final dual field theory conditions are described by these two quantum computational states. We first consider a complex Klein-Gordon field theory and argue that it can only be used to study the shortest quantum circuits which do not involve generators composed of tensor products of multiple Pauli Z matrices. Since such situation is not generic we call it the Z-problem. On the dual field theory side the Z-problem corresponds to massless excitations of the phase (Goldstone modes) that we attempt to fix using Higgs mechanism. The simplest dual theory which does not suffer from the massless excitation (or from the Z-problem) is the Abelian-Higgs model which we argue can be used for finding the shortest quantum circuits. Since every trajectory of the field theory is mapped directly to a quantum circuit, the shortest quantum circuits are identified with semiclassical trajectories. We also discuss the complexity of an actual algorithm that uses a dual theory prospective for solving the quantum maze problem and compare it with a geometric approach. We argue that it might be possible to solve the problem in sub-exponential time in 2 N , but for that we must consider the Klein-Gordon theory on curved spatial geometry and/or more complicated (than N

  12. The role of operator ordering in quantum field theory

    International Nuclear Information System (INIS)

    Suzuki, Tsuneo; Hirshfeld, A.C.; Leschke, H.

    1980-01-01

    We study the role of operator ordering in quantum field theory. Operator ordering techniques discussed in our previous papers in the quantum mechanical context are extended to field theory. In this case formally infinite terms appear which must be given a meaning in the framework of some definite regularization scheme. Different orderings for the non-commuting operators in the interaction Hamiltonian lead in general to different expressions for the Dyson-Wick expansion of the S-matrix, implying different Feynman rules. Different orderings correspond to different assignments for the initially undetermined values of the contractions occurring in closed-loop diagrams. Combining a special class of ordering schemes (u-ordering, a generalization of Weyl-ordering) with dimensional regularization leads to important simplifications, and in this case manipulations in which ordering complications are neglected may be justified. We use our methods to discuss gauge invariance in scalar electrodynamics, and the equivalent theorem for a reducible field theoretical model. (author)

  13. Information-theoretic limitations on approximate quantum cloning and broadcasting

    Science.gov (United States)

    Lemm, Marius; Wilde, Mark M.

    2017-07-01

    We prove quantitative limitations on any approximate simultaneous cloning or broadcasting of mixed states. The results are based on information-theoretic (entropic) considerations and generalize the well-known no-cloning and no-broadcasting theorems. We also observe and exploit the fact that the universal cloning machine on the symmetric subspace of n qudits and symmetrized partial trace channels are dual to each other. This duality manifests itself both in the algebraic sense of adjointness of quantum channels and in the operational sense that a universal cloning machine can be used as an approximate recovery channel for a symmetrized partial trace channel and vice versa. The duality extends to give control of the performance of generalized universal quantum cloning machines (UQCMs) on subspaces more general than the symmetric subspace. This gives a way to quantify the usefulness of a priori information in the context of cloning. For example, we can control the performance of an antisymmetric analog of the UQCM in recovering from the loss of n -k fermionic particles.

  14. Mean Field Analysis of Quantum Annealing Correction.

    Science.gov (United States)

    Matsuura, Shunji; Nishimori, Hidetoshi; Albash, Tameem; Lidar, Daniel A

    2016-06-03

    Quantum annealing correction (QAC) is a method that combines encoding with energy penalties and decoding to suppress and correct errors that degrade the performance of quantum annealers in solving optimization problems. While QAC has been experimentally demonstrated to successfully error correct a range of optimization problems, a clear understanding of its operating mechanism has been lacking. Here we bridge this gap using tools from quantum statistical mechanics. We study analytically tractable models using a mean-field analysis, specifically the p-body ferromagnetic infinite-range transverse-field Ising model as well as the quantum Hopfield model. We demonstrate that for p=2, where the phase transition is of second order, QAC pushes the transition to increasingly larger transverse field strengths. For p≥3, where the phase transition is of first order, QAC softens the closing of the gap for small energy penalty values and prevents its closure for sufficiently large energy penalty values. Thus QAC provides protection from excitations that occur near the quantum critical point. We find similar results for the Hopfield model, thus demonstrating that our conclusions hold in the presence of disorder.

  15. Classical Fields Derived from Quantum Sources.

    Science.gov (United States)

    Morris, Fred Gordon

    The Clifford algebra C(,4) is shown to be a suitable formalism for classical and quantum physics, and enables classical electromagnetic and gravitational field equations to be derived from the quantum conservation laws for electric charge and energy-momentum. The resulting linear theory of gravitation is shown to make predictions in agreement with the results of the classic weak field tests of gravitation theories. The C(,4) formalism is a physically intuitive, unifying, and mathematically powerful formalism. It can be developed as a geometric algebra in which its elements and operations have direct geometrical interpretations. The Dirac algebra of 4 x 4 matrices is a matrix representation of C(,4). C(,4) also contains the Pauli algebra, the generators of the Lorentz group, tensors, and differential forms. Because of these features C(,4) is both unifying, effectively merging tensor formulations of classical physics with the Dirac and Pauli algebras of quantum physics, and mathematically powerful, as its simple rules allow a wide variety of mathematical operations and structures to be defined. The unified treatment of classical and quantum physics permits a straightforward discussion of the classical limit of quantum field equations and conservation laws. Electromagnetic and gravitational field equations are derived from the local conservation laws for electric charge and energy-momentum by using the Poincare lemma from differential forms theory. The electromagnetic field equations thereby obtained are the usual Maxwell equations. The gravitational field equations obtained have an analogous mathematical form to the Maxwell equations and describe a linear gravitational field. The resulting theory provides a relativistic treatment of the motion of particles in a central gravitational field. The theory makes predictions in agreement with the predictions of general relativity for the classic weak field tests so can be considered a valid theory in problems in which the

  16. Negative power spectra in quantum field theory

    International Nuclear Information System (INIS)

    Hsiang, Jen-Tsung; Wu, Chun-Hsien; Ford, L.H.

    2011-01-01

    We consider the spatial power spectra associated with fluctuations of quadratic operators in field theory, such as quantum stress tensor components. We show that the power spectrum can be negative, in contrast to most fluctuation phenomena where the Wiener-Khinchin theorem requires a positive power spectrum. We show why the usual argument for positivity fails in this case, and discuss the physical interpretation of negative power spectra. Possible applications to cosmology are discussed. -- Highlights: → Wiener-Khinchin theorem usually implies a positive power spectrum of fluctuations. → We show this is not always the case in quantum field theory. → Quantum stress tensor fluctuations can have a negative power spectrum. → Negative power interchanges correlations and anticorrelations.

  17. Atomic focusing by quantum fields: Entanglement properties

    Energy Technology Data Exchange (ETDEWEB)

    Paz, I.G. da [Departamento de Física, Universidade Federal do Piauí, Campus Ministro Petrônio Portela, CEP 64049-550, Teresina, PI (Brazil); Frazão, H.M. [Universidade Federal do Piauí, Campus Profa. Cinobelina Elvas, CEP 64900-000, Bom Jesus, PI (Brazil); Departamento de Física, Instituto de Ciências Exatas, Universidade Federal de Minas Gerais, Caixa Postal 702, Belo Horizonte, MG 30123-970 (Brazil); Nemes, M.C. [Departamento de Física, Instituto de Ciências Exatas, Universidade Federal de Minas Gerais, Caixa Postal 702, Belo Horizonte, MG 30123-970 (Brazil); Peixoto de Faria, J.G. [Departamento de Física e Matemática, Centro Federal de Educação Tecnológica de Minas Gerais, Av. Amazonas 7675, Belo Horizonte, MG 30510-000 (Brazil)

    2014-04-01

    The coherent manipulation of the atomic matter waves is of great interest both in science and technology. In order to study how an atom optic device alters the coherence of an atomic beam, we consider the quantum lens proposed by Averbukh et al. [1] to show the discrete nature of the electromagnetic field. We extend the analysis of this quantum lens to the study of another essentially quantum property present in the focusing process, i.e., the atom–field entanglement, and show how the initial atomic coherence and purity are affected by the entanglement. The dynamics of this process is obtained in closed form. We calculate the beam quality factor and the trace of the square of the reduced density matrix as a function of the average photon number in order to analyze the coherence and purity of the atomic beam during the focusing process.

  18. Electronic properties of asymmetrical quantum dots dressed by laser field

    Energy Technology Data Exchange (ETDEWEB)

    Kibis, O.V. [Department of Applied and Theoretical Physics, Novosibirsk State Technical University, Karl Marx Avenue 20, 630092 Novosibirsk (Russian Federation); Slepyan, G.Ya.; Maksimenko, S.A. [Institute for Nuclear Problems, Belarus State University, Bobruyskaya St. 11, 220050 Minsk (Belarus); Hoffmann, A. [Institut fuer Festkoerperphysik, Technische Universitaet Berlin, Hardenbergstrasse 36, 10623 Berlin (Germany)

    2012-05-15

    In the present paper, we demonstrate theoretically that the strong non-resonant interaction between asymmetrical quantum dots (QDs) and a laser field results in harmonic oscillations of their band gap. It is shown that such oscillations change the spectrum of elementary electron excitations in QDs: in the absence of the laser pumping there is only one resonant electron frequency, but QDs dressed by the laser field have a set of electron resonant frequencies. One expects that this modification of elementary electron excitations in QDs can be observable in optical experiments. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  19. The Global Approach to Quantum Field Theory

    International Nuclear Information System (INIS)

    Folacci, Antoine; Jensen, Bruce

    2003-01-01

    Thanks to its impressive success in the second half of the 20th century, both in high-energy physics and in critical phenomena, quantum field theory has enjoyed an abundant literature. We therefore greet yet another book on this subject with caution: what can a monograph on quantum field theory bring now that is new, either conceptually or pedagogically? But when it is written by a physicist such as Bryce DeWitt, who has made his own contribution to the collection of field theory books with The Global Approach to Quantum Field Theory, all suspicion is naturally abandoned. DeWitt has made a formidable contribution to various areas of physics: general relativity, the interpretation of quantum mechanics, and most of all the quantization of non-Abelian gauge theories and quantum gravity. In addition, his pedagogical publications, especially the Les Houches schools of 1963 and 1983, have had a great impact on quantum field theory. We must begin by alerting the potential readers of this book that it cannot be compared to any other book in the field. This uniqueness applies to both the scientific content and the way the ideas are presented. For DeWitt, a central concept of field theory is that of 'space of histories'. For a field varphi i defined on a given spacetime M, the set of all varphi i (x) for all x in all charts of M defines its history. It is the space Phi of all possible histories (dynamically allowed or not) of the fields defined on M which is called the 'pace of histories' by DeWitt. If only bosonic fields are considered, the space of histories is an infinite-dimensional manifold and if fermionic fields are also present, it must be viewed as an infinite-dimensional supermanifold. The fields can then be regarded as coordinates on these structures, and the geometrical notions of differentiation, metric, connections, measure, as well as the geodesics which can be defined on it, are of fundamental importance in the development of the formalism of quantum field

  20. Lower Bound on the Energy Density in Classical and Quantum Field Theories.

    Science.gov (United States)

    Wall, Aron C

    2017-04-14

    A novel method for deriving energy conditions in stable field theories is described. In a local classical theory with one spatial dimension, a local energy condition always exists. For a relativistic field theory, one obtains the dominant energy condition. In a quantum field theory, there instead exists a quantum energy condition, i.e., a lower bound on the energy density that depends on information-theoretic quantities. Some extensions to higher dimensions are briefly discussed.

  1. Introductory lectures on quantum field theory

    International Nuclear Information System (INIS)

    Alvarez-Gaume, L.; Vasquez-Mozo, M.A.

    2011-01-01

    In these lectures we present a few topics in quantum field theory in detail. Some of them are conceptual and some more practical. They have been selected because they appear frequently in current applications to particle physics and string theory. (author)

  2. [Studies in quantum field theory: Progress report, April 1, 1991--March 31, 1992

    International Nuclear Information System (INIS)

    Bender, C.M.

    1992-01-01

    Professors Bender, Bernard, and Shrauner, Assistant Professors Ogilvie and Goltermann, Research Assistant Professors Visser and Petcher, and Research Associate Rivas are currently conducting research in many areas of high energy theoretical and mathematical physics. These areas include: lattice gauge calculations of masses and weak matrix elements; strong-coupling approximation; low-energy effective field theories; classical solutions of non-Abelian gauge theories; mean-field approximation in quantum field theory; path integral and coherent state representations in quantum field theory; the nature of perturbation theory in large order; quark condensation in QCD; chiral fermion theories on the lattice; the 1/N expansion in quantum field theory; effective potential and action in quantum field theories, including QCD; studies of the early universe and inflation; quantum gravity. This work is described in detail in the body of this proposal

  3. (Studies in quantum field theory: Progress report, April 1, 1991--March 31, 1992)

    Energy Technology Data Exchange (ETDEWEB)

    Bender, C M

    1992-01-01

    Professors Bender, Bernard, and Shrauner, Assistant Professors Ogilvie and Goltermann, Research Assistant Professors Visser and Petcher, and Research Associate Rivas are currently conducting research in many areas of high energy theoretical and mathematical physics. These areas include: lattice gauge calculations of masses and weak matrix elements; strong-coupling approximation; low-energy effective field theories; classical solutions of non-Abelian gauge theories; mean-field approximation in quantum field theory; path integral and coherent state representations in quantum field theory; the nature of perturbation theory in large order; quark condensation in QCD; chiral fermion theories on the lattice; the 1/N expansion in quantum field theory; effective potential and action in quantum field theories, including QCD; studies of the early universe and inflation; quantum gravity. This work is described in detail in the body of this proposal.

  4. Energy levels and quantum states of [Leu]enkephalin conformations based on theoretical and experimental investigations

    DEFF Research Database (Denmark)

    Abdali, Salim; Jensen, Morten Østergaard; Bohr, Henrik

    2003-01-01

    This paper describes a theoretical and experimental study of [Leu]enkephalin conformations with respect to the quantum estates of the atomic structure of the peptide. Results from vibrational absorption measurements and quantum calculations are used to outline a quantum picture and to assign vibr...

  5. Quantum field theory in curved spacetime

    International Nuclear Information System (INIS)

    Gibbons, G.W.

    1978-04-01

    The purpose of this article is to outline what the extension of such a treatment to curved space entails and to discuss what essentially new features arise when one takes into account the quantum mechanical nature of gravitating systems. I shall throughout assume a classical, unquantized gravitational field and confine the discussion to matter fields although similar techniques and ideas may be applied to 'gravitons' - that is linearized perturbations of the metric propagating on some fixed, unperturbed, background. (orig./WL) [de

  6. Metric quantum field theory: A preliminary look

    International Nuclear Information System (INIS)

    Watson, W.N.

    1988-01-01

    Spacetime coordinates are involved in uncertainty relations; spacetime itself appears to exhibit curvature. Could the continua associated with field variables exhibit curvature? This question, as well as the ideas that (a) difficulties with quantum theories of gravitation may be due to their formulation in an incorrect analogy with other quantum field theories, (b) spacetime variables should not be any more basic than others for describing physical phenomena, and (c) if field continua do not exhibit curvature, the reasons would be of interest, motivated the formulation of a theory of variable curvature and torsion in the electromagnetic four-potential's reciprocal space. Curvature and torsion equation completely analogous to those for a gauge theory of gravitation (the Einstein-Cartan-Sciama-Kibble theory) are assumed for this continuum. The interaction-Hamiltonian density of this theory, to a first approximation, implies that in addition to the Maxwell-Dirac field interaction of ordinary quantum electrodynamics, there should also be an interaction between Dirac-field vector and pseudovector currents unmediated by photons, as well as other interactions involving two or three Dirac-field currents interacting with the Maxwell field at single spacetime events. Calculations expressing Bhabha-scattering cross sections for incident beams with parallel spins differ from those of unmodified quantum electrodynamics by terms of first order in the gravitational constant of the theory, but the corresponding cross section for unpolarized incident beams differs from that of the unmodified theory only by terms of higher order in that constant. Undesirable features of the present theory include its nonrenormalizability, the obscurity of the meaning of its inverse field operator, and its being based on electrodynamics rather than electroweak dynamics

  7. Schrodinger representation in renormalizable quantum field theory

    International Nuclear Information System (INIS)

    Symanzik, K.

    1983-01-01

    The problem of the Schrodinger representation arose from work on the Nambu-Goto Ansatz for integration over surfaces. Going beyond semiclassical approximation leads to two problems of nonrenormalizibility and of whether Dirichlet boundary conditions can be imposed on a ''Euclidean'' quantum field theory. The Schrodinger representation is constructed in a way where the principles of general renormalization theory can be refered to. The Schrodinger function of surface terms is studied, as well as behaviour at the boundary. The Schrodinger equation is derived. Completeness, unitarity, and computation of expectation values are considered. Extensions of these methods into other Bose field theories such as Fermi fields and Marjorana fields is straightforward

  8. Local algebras in Euclidean quantum field theory

    International Nuclear Information System (INIS)

    Guerra, Francesco.

    1975-06-01

    The general structure of the local observable algebras of Euclidean quantum field theory is described, considering the very simple examples of the free scalar field, the vector meson field, and the electromagnetic field. The role of Markov properties, and the relations between Euclidean theory and Hamiltonian theory in Minkowski space-time are especially emphasized. No conflict appears between covariance (in the Euclidean sense) and locality (in the Markov sense) on one hand and positive definiteness of the metric on the other hand [fr

  9. Non standard analysis, polymer models, quantum fields

    International Nuclear Information System (INIS)

    Albeverio, S.

    1984-01-01

    We give an elementary introduction to non standard analysis and its applications to the theory of stochastic processes. This is based on a joint book with J.E. Fenstad, R. Hoeegh-Krohn and T. Lindstroeem. In particular we give a discussion of an hyperfinite theory of Dirichlet forms with applications to the study of the Hamiltonian for a quantum mechanical particle in the potential created by a polymer. We also discuss new results on the existence of attractive polymer measures in dimension d 1 2 phi 2 2 )sub(d)-model of interacting quantum fields. (orig.)

  10. Gallilei covariant quantum mechanics in electromagnetic fields

    Directory of Open Access Journals (Sweden)

    H. E. Wilhelm

    1985-01-01

    Full Text Available A formulation of the quantum mechanics of charged particles in time-dependent electromagnetic fields is presented, in which both the Schroedinger equation and wave equations for the electromagnetic potentials are Galilei covariant, it is shown that the Galilean relativity principle leads to the introduction of the electromagnetic substratum in which the matter and electromagnetic waves propagate. The electromagnetic substratum effects are quantitatively significant for quantum mechanics in reference frames, in which the substratum velocity w is in magnitude comparable with the velocity of light c. The electromagnetic substratum velocity w occurs explicitly in the wave equations for the electromagnetic potentials but not in the Schroedinger equation.

  11. Statistical approach to quantum field theory. An introduction

    Energy Technology Data Exchange (ETDEWEB)

    Wipf, Andreas [Jena Univ. (Germany). Theoretisch-Physikalisches Inst.

    2013-02-01

    Based on course-tested notes and pedagogical in style. Authored by a leading researcher in the field. Contains end-of-chapter problems and listings of short, useful computer programs. Authored by a leading researcher in the field. Contains end-of-chapter problems and listings of short, useful computer programs. Contains end-of-chapter problems and listings of short, useful computer programs. Over the past few decades the powerful methods of statistical physics and Euclidean quantum field theory have moved closer together, with common tools based on the use of path integrals. The interpretation of Euclidean field theories as particular systems of statistical physics has opened up new avenues for understanding strongly coupled quantum systems or quantum field theories at zero or finite temperatures. Accordingly, the first chapters of this book contain a self-contained introduction to path integrals in Euclidean quantum mechanics and statistical mechanics. The resulting high-dimensional integrals can be estimated with the help of Monte Carlo simulations based on Markov processes. The most commonly used algorithms are presented in detail so as to prepare the reader for the use of high-performance computers as an ''experimental'' tool for this burgeoning field of theoretical physics. Several chapters are then devoted to an introduction to simple lattice field theories and a variety of spin systems with discrete and continuous spins, where the ubiquitous Ising model serves as an ideal guide for introducing the fascinating area of phase transitions. As an alternative to the lattice formulation of quantum field theories, variants of the flexible renormalization group methods are discussed in detail. Since, according to our present-day knowledge, all fundamental interactions in nature are described by gauge theories, the remaining chapters of the book deal with gauge theories without and with matter. This text is based on course-tested notes for graduate

  12. Statistical approach to quantum field theory. An introduction

    International Nuclear Information System (INIS)

    Wipf, Andreas

    2013-01-01

    Based on course-tested notes and pedagogical in style. Authored by a leading researcher in the field. Contains end-of-chapter problems and listings of short, useful computer programs. Authored by a leading researcher in the field. Contains end-of-chapter problems and listings of short, useful computer programs. Contains end-of-chapter problems and listings of short, useful computer programs. Over the past few decades the powerful methods of statistical physics and Euclidean quantum field theory have moved closer together, with common tools based on the use of path integrals. The interpretation of Euclidean field theories as particular systems of statistical physics has opened up new avenues for understanding strongly coupled quantum systems or quantum field theories at zero or finite temperatures. Accordingly, the first chapters of this book contain a self-contained introduction to path integrals in Euclidean quantum mechanics and statistical mechanics. The resulting high-dimensional integrals can be estimated with the help of Monte Carlo simulations based on Markov processes. The most commonly used algorithms are presented in detail so as to prepare the reader for the use of high-performance computers as an ''experimental'' tool for this burgeoning field of theoretical physics. Several chapters are then devoted to an introduction to simple lattice field theories and a variety of spin systems with discrete and continuous spins, where the ubiquitous Ising model serves as an ideal guide for introducing the fascinating area of phase transitions. As an alternative to the lattice formulation of quantum field theories, variants of the flexible renormalization group methods are discussed in detail. Since, according to our present-day knowledge, all fundamental interactions in nature are described by gauge theories, the remaining chapters of the book deal with gauge theories without and with matter. This text is based on course-tested notes for graduate students and, as

  13. Integrable structures in quantum field theory

    International Nuclear Information System (INIS)

    Negro, Stefano

    2016-01-01

    This review was born as notes for a lecture given at the Young Researchers Integrability School (YRIS) school on integrability in Durham, in the summer of 2015. It deals with a beautiful method, developed in the mid-nineties by Bazhanov, Lukyanov and Zamolodchikov and, as such, called BLZ. This method can be interpreted as a field theory version of the quantum inverse scattering, also known as the algebraic Bethe ansatz. Starting with the case of conformal field theories (CFTs) we show how to build the field theory analogues of commuting transfer T matrices and Baxter Q -operators of integrable lattice models. These objects contain the complete information of the integrable structure of the theory, viz. the integrals of motion, and can be used, as we will show, to derive the thermodynamic Bethe ansatz and nonlinear integral equations. This same method can be easily extended to the description of integrable structures of certain particular massive deformations of CFTs; these, in turn, can be described as quantum group reductions of the quantum sine-Gordon model and it is an easy step to include this last theory in the framework of BLZ approach. Finally we show an interesting and surprising connection of the BLZ structures with classical objects emerging from the study of classical integrable models via the inverse scattering transform method. This connection goes under the name of ODE/IM correspondence and we will present it for the specific case of quantum sine-Gordon model only. (topical review)

  14. Quantum wells, wires and dots theoretical and computational physics of semiconductor nanostructures

    CERN Document Server

    Harrison, Paul

    2016-01-01

    Quantum Wells, Wires and Dots provides all the essential information, both theoretical and computational, to develop an understanding of the electronic, optical and transport properties of these semiconductor nanostructures. The book will lead the reader through comprehensive explanations and mathematical derivations to the point where they can design semiconductor nanostructures with the required electronic and optical properties for exploitation in these technologies. This fully revised and updated 4th edition features new sections that incorporate modern techniques and extensive new material including: - Properties of non-parabolic energy bands - Matrix solutions of the Poisson and Schrodinger equations - Critical thickness of strained materials - Carrier scattering by interface roughness, alloy disorder and impurities - Density matrix transport modelling -Thermal modelling Written by well-known authors in the field of semiconductor nanostructures and quantum optoelectronics, this user-friendly guide is pr...

  15. Geophysical field disturbances and quantum mechanics

    Science.gov (United States)

    Kuznetsov, Vladimir

    2017-10-01

    Quantum processes impact into physics of geophysical field disturbances is discussed here in examples of phenomena such as an earthquake with processes preceding and accompanying it, volcanoes eruptions and diamond exploding pipes. Physics of shock waves generation in ionosphere and atmosphere, mechanism of atmosphere phenomena in supercooled clouds recorded by a stormglass is considered. The report treats of physics of ball and dark lightning, of generating in atmosphere the high-energy particles involved in sprites occurrence, and so on. Geophysical phenomena considered here have no clear and consistent interpretation in the context of classical physics. We attempt to involve the recent achievements of quantum physics namely the quantum entanglement between elementary particles implicated in considered phenomena.

  16. Factorization algebras in quantum field theory

    CERN Document Server

    Costello, Kevin

    2017-01-01

    Factorization algebras are local-to-global objects that play a role in classical and quantum field theory which is similar to the role of sheaves in geometry: they conveniently organize complicated information. Their local structure encompasses examples like associative and vertex algebras; in these examples, their global structure encompasses Hochschild homology and conformal blocks. In this first volume, the authors develop the theory of factorization algebras in depth, but with a focus upon examples exhibiting their use in field theory, such as the recovery of a vertex algebra from a chiral conformal field theory and a quantum group from Abelian Chern-Simons theory. Expositions of the relevant background in homological algebra, sheaves and functional analysis are also included, thus making this book ideal for researchers and graduates working at the interface between mathematics and physics.

  17. Introduction to algebraic quantum field theory

    International Nuclear Information System (INIS)

    Horuzhy, S.S.

    1990-01-01

    This volume presents a systematic introduction to the algebraic approach to quantum field theory. The structure of the contents corresponds to the way the subject has advanced. It is shown how the algebraic approach has developed from the purely axiomatic theory of observables via superselection rules into the dynamical formalism of fields and observables. Chapter one discusses axioms and their consequences -many of which are now classical theorems- and deals, in general, with the axiomatic theory of local observable algebras. The absence of field concepts makes this theory incomplete and, in chapter two, superselection rules are shown to be the key to the reconstruction of fields from observables. Chapter three deals with the algebras of Wightman fields, first unbounded operator algebras, then Von Neumann field algebras (with a special section on wedge region algebras) and finally local algebras of free and generalised free fields. (author). 447 refs.; 4 figs

  18. Quantum fields in curved space-times

    International Nuclear Information System (INIS)

    Ashtekar, A.; Magnon, A.

    1975-01-01

    The problem of obtaining a quantum description of the (real) Klein-Gordon system in a given curved space-time is discussed. An algebraic approach is used. The *-algebra of quantum operators is constructed explicitly and the problem of finding its *-representation is reduced to that of selecting a suitable complex structure on the real vector space of the solutions of the (classical) Klein-Gordon equation. Since, in a static space-time, there already exists, a satisfactory quantum field theory, in this case one already knows what the 'correct' complex structure is. A physical characterization of this 'correct' complex structure is obtained. This characterization is used to extend quantum field theory to non-static space-times. Stationary space-times are considered first. In this case, the issue of extension is completely straightforward and the resulting theory is the natural generalization of the one in static space-times. General, non-stationary space-times are then considered. In this case the issue of extension is quite complicated and only a plausible extension is presented. Although the resulting framework is well-defined mathematically, the physical interpretation associated with it is rather unconventional. Merits and weaknesses of this framework are discussed. (author)

  19. Undergraduate Lecture Notes in Topological Quantum Field Theory

    OpenAIRE

    Ivancevic, Vladimir G.; Ivancevic, Tijana T.

    2008-01-01

    These third-year lecture notes are designed for a 1-semester course in topological quantum field theory (TQFT). Assumed background in mathematics and physics are only standard second-year subjects: multivariable calculus, introduction to quantum mechanics and basic electromagnetism. Keywords: quantum mechanics/field theory, path integral, Hodge decomposition, Chern-Simons and Yang-Mills gauge theories, conformal field theory

  20. On single-time reduction in quantum field theory

    International Nuclear Information System (INIS)

    Arkhipov, A.A.

    1984-01-01

    It is shown, how the causality and spectrality properties in qUantum field theory may help one to carry out a single-time reduction of the Bethe-Salpeter wave fUnction. The single-time reduction technique is not based on any concrete model of the quantum field theory. Axiomatic formulations underline the quantum field theory

  1. Classical gravity and quantum matter fields in unified field theory

    Science.gov (United States)

    von Borzeszkowski, Horst-Heino; Treder, Hans-Jürgen

    1996-01-01

    The Einstein-Schrödinger purely affine field theory of the non-symmetric field provides canonical field equations without constraints. These equations imply the Heisenberg-Pauli commutation rules of quantum field theory. In the Schrödinger gauging of the Einstein field coordinatesU {/kl i }=Γ{/kl i }-δ{/l i }Γ{/km m }, this unified geometric field theory becomes a model of the coupling between a quantized Maxwellian field in a medium and classical gravity. Therefore, independently of the question as to the physical truth of this model, its analysis performed in the present paper demonstrates that, in the framework of a quantized unified field theory, gravity can appear as a genuinely classical field.

  2. Clifford algebra in finite quantum field theories

    International Nuclear Information System (INIS)

    Moser, M.

    1997-12-01

    We consider the most general power counting renormalizable and gauge invariant Lagrangean density L invariant with respect to some non-Abelian, compact, and semisimple gauge group G. The particle content of this quantum field theory consists of gauge vector bosons, real scalar bosons, fermions, and ghost fields. We assume that the ultimate grand unified theory needs no cutoff. This yields so-called finiteness conditions, resulting from the demand for finite physical quantities calculated by the bare Lagrangean. In lower loop order, necessary conditions for finiteness are thus vanishing beta functions for dimensionless couplings. The complexity of the finiteness conditions for a general quantum field theory makes the discussion of non-supersymmetric theories rather cumbersome. Recently, the F = 1 class of finite quantum field theories has been proposed embracing all supersymmetric theories. A special type of F = 1 theories proposed turns out to have Yukawa couplings which are equivalent to generators of a Clifford algebra representation. These algebraic structures are remarkable all the more than in the context of a well-known conjecture which states that finiteness is maybe related to global symmetries (such as supersymmetry) of the Lagrangean density. We can prove that supersymmetric theories can never be of this Clifford-type. It turns out that these Clifford algebra representations found recently are a consequence of certain invariances of the finiteness conditions resulting from a vanishing of the renormalization group β-function for the Yukawa couplings. We are able to exclude almost all such Clifford-like theories. (author)

  3. The Global Approach to Quantum Field Theory

    Energy Technology Data Exchange (ETDEWEB)

    Folacci, Antoine; Jensen, Bruce [Faculte des Sciences, Universite de Corse (France); Department of Mathematics, University of Southampton (United Kingdom)

    2003-12-12

    Thanks to its impressive success in the second half of the 20th century, both in high-energy physics and in critical phenomena, quantum field theory has enjoyed an abundant literature. We therefore greet yet another book on this subject with caution: what can a monograph on quantum field theory bring now that is new, either conceptually or pedagogically? But when it is written by a physicist such as Bryce DeWitt, who has made his own contribution to the collection of field theory books with The Global Approach to Quantum Field Theory, all suspicion is naturally abandoned. DeWitt has made a formidable contribution to various areas of physics: general relativity, the interpretation of quantum mechanics, and most of all the quantization of non-Abelian gauge theories and quantum gravity. In addition, his pedagogical publications, especially the Les Houches schools of 1963 and 1983, have had a great impact on quantum field theory. We must begin by alerting the potential readers of this book that it cannot be compared to any other book in the field. This uniqueness applies to both the scientific content and the way the ideas are presented. For DeWitt, a central concept of field theory is that of 'space of histories'. For a field varphi{sup i} defined on a given spacetime M, the set of all varphi{sup i}(x) for all x in all charts of M defines its history. It is the space Phi of all possible histories (dynamically allowed or not) of the fields defined on M which is called the 'pace of histories' by DeWitt. If only bosonic fields are considered, the space of histories is an infinite-dimensional manifold and if fermionic fields are also present, it must be viewed as an infinite-dimensional supermanifold. The fields can then be regarded as coordinates on these structures, and the geometrical notions of differentiation, metric, connections, measure, as well as the geodesics which can be defined on it, are of fundamental importance in the development of the

  4. Structural aspects of quantum field theory and noncommutative geometry

    CERN Document Server

    Grensing, Gerhard

    2013-01-01

    This book is devoted to the subject of quantum field theory. It is divided into two volumes. The first can serve as a textbook on the main techniques and results of quantum field theory, while the second treats more recent developments, in particular the subject of quantum groups and noncommutative geometry, and their interrelation. The first volume is directed at graduate students who want to learn the basic facts about quantum field theory. It begins with a gentle introduction to classical field theory, including the standard model of particle physics, general relativity, and also supergravity. The transition to quantized fields is performed with path integral techniques, by means of which the one-loop renormalization of a self-interacting scalar quantum field, of quantum electrodynamics, and the asymptotic freedom of quantum chromodynamics is treated. In the last part of the first volume, the application of path integral methods to systems of quantum statistical mechanics is covered. The book ends with a r...

  5. Quantum Ising chains with boundary fields

    International Nuclear Information System (INIS)

    Campostrini, Massimo; Vicari, Ettore; Pelissetto, Andrea

    2015-01-01

    We present a detailed study of the finite one-dimensional quantum Ising chain in a transverse field in the presence of boundary magnetic fields coupled with the order-parameter spin operator. We consider two magnetic fields located at the boundaries of the chain that have the same strength and that are aligned in the same or in the opposite direction. We derive analytic expressions for the gap in all phases for large values of the chain length L, as a function of the boundary field strength. We also investigate the behaviour of the chain in the quantum ferromagnetic phase for oppositely aligned fields, focusing on the magnet-to-kink transition that occurs at a finite value of the magnetic field strength. At this transition we compute analytically the finite-size crossover functions for the gap, the magnetisation profile, the two-point correlation function, and the density of fermionic modes. As the magnet-to-kink transition is equivalent to the wetting transition in two-dimensional classical Ising models, our results provide new analytic predictions for the finite-size behaviour of Ising systems in a strip geometry at this transition. (paper)

  6. Quantum field theory and phase transitions: universality and renormalization group

    International Nuclear Information System (INIS)

    Zinn-Justin, J.

    2003-08-01

    In the quantum field theory the problem of infinite values has been solved empirically through a method called renormalization, this method is satisfying only in the framework of renormalization group. It is in the domain of statistical physics and continuous phase transitions that these issues are the easiest to discuss. Within the framework of a course in theoretical physics the author introduces the notions of continuous limits and universality in stochastic systems operating with a high number of freedom degrees. It is shown that quasi-Gaussian and mean field approximation are unable to describe phase transitions in a satisfying manner. A new concept is required: it is the notion of renormalization group whose fixed points allow us to understand universality beyond mean field. The renormalization group implies the idea that long distance correlations near the transition temperature might be described by a statistical field theory that is a quantum field in imaginary time. Various forms of renormalization group equations are presented and solved in particular boundary limits, namely for fields with high numbers of components near the dimensions 4 and 2. The particular case of exact renormalization group is also introduced. (A.C.)

  7. Entanglement in the harmonic chain and quantum fields

    International Nuclear Information System (INIS)

    Kofler, J.; Vedral, V.; Brukner, C.

    2005-01-01

    Full text: Relativistic field theory is a natural basis for the theoretical investigation of quantum entanglement, since the concept of locality and causality is inherently included. Vacuum entanglement of relativistic fields manifests itself in Hawking radiation and the Unruh effect. But it also is encountered in the linear harmonic chain, which - in the continuum limit and if generalized to three spatial dimensions - becomes the real scalar Klein-Gordon field. One can define average position and momentum operators for two separated blocks of oscillators in the harmonic chain and investigate the entanglement - by means of a separability criterion - between these blocks as a function of their distance and the coupling between the oscillators. This motivated us to rewrite the general separability conditions for continuous variables into the language of quantum field theory, where the position and momentum operator become integrals of the Klein-Gordon field and the conjugate momentum field, respectively. The role of the modes (or particles) is then merely played by the space(-time) regions over which the integration takes (author)

  8. On quantum field theory in gravitational background

    International Nuclear Information System (INIS)

    Haag, R.; Narnhofer, H.; Stein, U.

    1984-02-01

    We discuss Quantum Fields on Riemannian space-time. A principle of local definitness is introduced which is needed beyond equations of motion and commutation relations to fix the theory uniquely. It also allows to formulate local stability. In application to a region with a time-like Killing vector field and horizons it yields the value of the Hawking temperature. The concept of vacuum and particles in a non stationary metric is treated in the example of the Robertson-Walker metric and some remarks on detectors in non inertial motion are added. (orig.)

  9. On space of integrable quantum field theories

    Directory of Open Access Journals (Sweden)

    F.A. Smirnov

    2017-02-01

    Full Text Available We study deformations of 2D Integrable Quantum Field Theories (IQFT which preserve integrability (the existence of infinitely many local integrals of motion. The IQFT are understood as “effective field theories”, with finite ultraviolet cutoff. We show that for any such IQFT there are infinitely many integrable deformations generated by scalar local fields Xs, which are in one-to-one correspondence with the local integrals of motion; moreover, the scalars Xs are built from the components of the associated conserved currents in a universal way. The first of these scalars, X1, coincides with the composite field (TT¯ built from the components of the energy–momentum tensor. The deformations of quantum field theories generated by X1 are “solvable” in a certain sense, even if the original theory is not integrable. In a massive IQFT the deformations Xs are identified with the deformations of the corresponding factorizable S-matrix via the CDD factor. The situation is illustrated by explicit construction of the form factors of the operators Xs in sine-Gordon theory. We also make some remarks on the problem of UV completeness of such integrable deformations.

  10. Theoretical investigation of magnetic property in paramagnetic neodymium gallium garnet under high magnetic field

    International Nuclear Information System (INIS)

    Wang Wei; Liu Gongqiang; Wang Jinhui

    2006-01-01

    The magnetic property in neodymium gallium garnet (NdGaG) is studied by the quantum theory. The ground configuration split states are calculated taking into account the spin-orbit interaction and crystal field effect. Taking account of the Nd-Nd exchange interaction, a good agreement between experimental and theoretical values can be obtained for the variation of the magnetic moment with the external magnetic field under 'extreme' conditions (low temperature and high magnetic field). Moreover, the temperature dependence of magnetic moment and the magnetic susceptibility χ is also discussed. Above 30 K, the magnetization (M) shows a linear field (H e ) dependence

  11. Quantum Fields, Dark Matter and Non-Standard Wigner Classes

    Science.gov (United States)

    Gillard, A. B.; Martin, B. M. S.

    2010-12-01

    The Elko field of Ahluwalia and Grumiller is a quantum field for massive spin-1/2 particles. It has been suggested as a candidate for dark matter. We discuss our attempts to interpret the Elko field as a quantum field in the sense of Weinberg. Our work suggests that one should investigate quantum fields based on representations of the full Poincaré group which belong to one of the non-standard Wigner classes.

  12. Thermo field dynamics: a quantum field theory at finite temperature

    International Nuclear Information System (INIS)

    Mancini, F.; Marinaro, M.; Matsumoto, H.

    1988-01-01

    A brief review of the theory of thermo field dynamics (TFD) is presented. TFD is introduced and developed by Umezawa and his coworkers at finite temperature. The most significant concept in TFD is that of a thermal vacuum which satisfies some conditions denoted as thermal state conditions. The TFD permits to reformulate theories at finite temperature. There is no need in an additional principle to determine particle distributions at T ≠ 0. Temperature and other macroscopic parameters are introduced in the definition of the vacuum state. All operator formalisms used in quantum field theory at T=0 are preserved, although the field degrees of freedom are doubled. 8 refs

  13. Advanced field theoretic simulations of polymer nanocomposites

    Science.gov (United States)

    Koski, Jason

    Polymers nanocomposites (PNCs) have emerged as a promising class of materials that can exhibit enhanced mechanical, optical, and electrical properties over polymers or nanoparticles alone. The outstanding issue is that the parameter space associated with PNCs is vast and a global framework for what parameters and processing conditions determine the resulting structure is lacking. Polymer field theory has been established as the primary tool in understanding inhomogeneous polymer systems. Here, we extend the polymer field theory framework to efficiently model PNCs, which we refer to as polymer nanocomposite field theory (PNC-FT). The utility of the PNC-FT method is the ability to efficiently study the thermodynamics and vast parameter space associated with PNCs. The PNC-FT method is developed to efficiently model a wide array of systems: nanospheres, nanorods, grafted nanoparticles with simple (homopolymer) and complex (diblock, mixed, and Janus) grafting architectures. Moreover, a numerical dynamic mean-field theory (DMFT) is presented as an additional tool to capture non-equilibrium behavior in PNC systems. The PNC-FT framework is validated through comparisons with Monte Carlo simulations and by demonstrations of the ability to capture particle correlations, a feature that is not captured in the conventional polymer field theory framework. The PNC-FT method is used to study: the ideal domain spacing of lamellar forming block copolymer nanocomposites, the segregation of homopolymers and nanoparticles to tilt grain boundaries in block copolymer thin films, complex grafted nanoparticles acting as surfactants in a homopolymer blend, and grafted gold nanorods in polymer thin films. The grafted gold nanorod study is done in direct collaboration with experimentalists where we provide an additional systematic study that demonstrates the advantages and disadvantages of: a previously developed hybrid particle-field theory (HPFT), PNC-FT, and DMFT. In investigating this wide

  14. Nonequilibrium fermion production in quantum field theory

    Energy Technology Data Exchange (ETDEWEB)

    Pruschke, Jens

    2010-06-16

    The creation of matter in the early universe or in relativistic heavy-ion collisions is inevitable connected to nonequilibrium physics. One of the key challenges is the explanation of the corresponding thermalization process following nonequilibrium instabilities. The role of fermionic quantum fields in such scenarios is discussed in the literature by using approximations of field theories which neglect important quantum corrections. This thesis goes beyond such approximations. A quantum field theory where scalar bosons interact with Dirac fermions via a Yukawa coupling is analyzed in the 2PI effective action formalism. The chosen approximation allows for a correct description of the dynamics including nonequilibrium instabilities. In particular, fermion-boson loop corrections allow to study the interaction of fermions with large boson fluctuations. The applied initial conditions generate nonequilibrium instabilities like parametric resonance or spinodal instabilities. The equations of motion for correlation functions are solved numerically and major characteristics of the fermion dynamics are described by analytical solutions. New mechanisms for the production of fermions are found. Simulations in the case of spinodal instability show that unstable boson fluctuations induce exponentially growing fermion modes with approximately the same growth rate. If the unstable regime lasts long enough a thermalization of the infrared part of the fermion occupation number occurs on time scales much shorter than the time scale on which bosonic quantum fields thermalize. Fermions acquire an excess of occupation in the ultraviolet regime compared to a Fermi-Dirac statistic characterized by a power-law with exponent two. The fermion production mechanism via parametric resonance is found to be most efficient after the instability ends. Quantum corrections then provide a very efficient particle creation mechanism which is interpreted as an amplification of decay processes. The ratio

  15. On the field theoretic description of gravitation

    NARCIS (Netherlands)

    Nieuwenhuizen, T.M.; Kleinert, H.; Jantzen, R.T.; Ruffini, R.

    2008-01-01

    Maxwell started to describe gravitation as a field in Minkowski space. Such an approach brought Babak and Grishchuk in 1999 the gravitational energy-momentum tensor. Simple manipulations allow the Einstein equations to take the form Aµν = (8πG/c4)Θµν, where A is the acceleration tensor and Θ, the

  16. Quantum curves and conformal field theory

    Science.gov (United States)

    Manabe, Masahide; Sułkowski, Piotr

    2017-06-01

    To a given algebraic curve we assign an infinite family of quantum curves (Schrödinger equations), which are in one-to-one correspondence with, and have the structure of, Virasoro singular vectors. For a spectral curve of a matrix model we build such quantum curves out of an appropriate representation of the Virasoro algebra, encoded in the structure of the α /β -deformed matrix integral and its loop equation. We generalize this construction to a large class of algebraic curves by means of a refined topological recursion. We also specialize this construction to various specific matrix models with polynomial and logarithmic potentials, and among other results, show that various ingredients familiar in the study of conformal field theory (Ward identities, correlation functions and a representation of Virasoro operators acting thereon, Belavin-Polyakov-Zamolodchikov equations) arise upon specialization of our formalism to the multi-Penner matrix model.

  17. Non equilibrium quantum fields in cosmology

    International Nuclear Information System (INIS)

    Paz, J.P.

    1991-01-01

    The authors discuss the general framework used to construct a quantum mechanical model of the inflationary phase transition. The emer-gence of classical behavior in the longwavelength modes of the inflation is one of the facts that these models should address. For some toy examples (in which the inflation interacts with an environment consti-tuted by other fields) decoherence is shown of the modes with physical wavelength greater than the horizon. The authors use an approach based on a master equation. They take advantage of the similarities that exist between the master equation for the toy cosmological models and the one for the simple Quantum Brownian Motion. Recent results are discussed obtained for the general QBM problem (in which the environment has a generic spectral density). (author). 10 refs

  18. A Quantum Theoretical Explanation for Probability Judgment Errors

    Science.gov (United States)

    Busemeyer, Jerome R.; Pothos, Emmanuel M.; Franco, Riccardo; Trueblood, Jennifer S.

    2011-01-01

    A quantum probability model is introduced and used to explain human probability judgment errors including the conjunction and disjunction fallacies, averaging effects, unpacking effects, and order effects on inference. On the one hand, quantum theory is similar to other categorization and memory models of cognition in that it relies on vector…

  19. Instantons and large N an introduction to non-perturbative methods in quantum field theory

    CERN Document Server

    Marino, Marcos

    2015-01-01

    This highly pedagogical textbook for graduate students in particle, theoretical and mathematical physics, explores advanced topics of quantum field theory. Clearly divided into two parts; the first focuses on instantons with a detailed exposition of instantons in quantum mechanics, supersymmetric quantum mechanics, the large order behavior of perturbation theory, and Yang-Mills theories, before moving on to examine the large N expansion in quantum field theory. The organised presentation style, in addition to detailed mathematical derivations, worked examples and applications throughout, enables students to gain practical experience with the tools necessary to start research. The author includes recent developments on the large order behaviour of perturbation theory and on large N instantons, and updates existing treatments of classic topics, to ensure that this is a practical and contemporary guide for students developing their understanding of the intricacies of quantum field theory.

  20. A relativistic theory for continuous measurement of quantum fields

    International Nuclear Information System (INIS)

    Diosi, L.

    1990-04-01

    A formal theory for the continuous measurement of relativistic quantum fields is proposed. The corresponding scattering equations were derived. The proposed formalism reduces to known equations in the Markovian case. Two recent models for spontaneous quantum state reduction have been recovered in the framework of this theory. A possible example of the relativistic continuous measurement has been outlined in standard Quantum Electrodynamics. The continuous measurement theory possesses an alternative formulation in terms of interacting quantum and stochastic fields. (author) 23 refs

  1. A general field-covariant formulation of quantum field theory

    International Nuclear Information System (INIS)

    Anselmi, Damiano

    2013-01-01

    In all nontrivial cases renormalization, as it is usually formulated, is not a change of integration variables in the functional integral, plus parameter redefinitions, but a set of replacements, of actions and/or field variables and parameters. Because of this, we cannot write simple identities relating bare and renormalized generating functionals, or generating functionals before and after nonlinear changes of field variables. In this paper we investigate this issue and work out a general field-covariant approach to quantum field theory, which allows us to treat all perturbative changes of field variables, including the relation between bare and renormalized fields, as true changes of variables in the functional integral, under which the functionals Z and W=lnZ behave as scalars. We investigate the relation between composite fields and changes of field variables, and we show that, if J are the sources coupled to the elementary fields, all changes of field variables can be expressed as J-dependent redefinitions of the sources L coupled to the composite fields. We also work out the relation between the renormalization of variable-changes and the renormalization of composite fields. Using our transformation rules it is possible to derive the renormalization of a theory in a new variable frame from the renormalization in the old variable frame, without having to calculate it anew. We define several approaches, useful for different purposes, in particular a linear approach where all variable changes are described as linear source redefinitions. We include a number of explicit examples. (orig.)

  2. Renormalization and Interaction in Quantum Field Theory

    International Nuclear Information System (INIS)

    RATSIMBARISON, H.M.

    2008-01-01

    This thesis works on renormalization in quantum field theory (QFT), in order to show the relevance of some mathematical structures as C*-algebraic and probabilistic structures. Our work begins with a study of the path integral formalism and the Kreimer-Connes approach in perturbative renormalization, which allows to situate the statistical nature of QFT and to appreciate the ultra-violet divergence problem of its partition function. This study is followed by an emphasis of the presence of convolution products in non perturbative renormalisation, through the construction of the Wilson effective action and the Legendre effective action. Thanks to these constructions and the definition of effective theories according J. Polchinski, the non perturbative renormalization shows in particular the general approach of regularization procedure. We begin the following chapter with a C*-algebraic approach of the scale dependence of physical theories by showing the existence of a hierarchy of commutative spaces of states and its compatibility with the fiber bundle formulation of classical field theory. Our Hierarchy also allows us to modelize the notion of states and particles. Finally, we develop a probabilistic construction of interacting theories starting from simple model, a Bernoulli random processes. We end with some arguments on the applicability of our construction -such as the independence between the free and interacting terms and the possibility to introduce a symmetry group wich will select the type of interactions in quantum field theory. [fr

  3. Boundaries immersed in a scalar quantum field

    International Nuclear Information System (INIS)

    Actor, A.A.; Bender, I.

    1996-01-01

    We study the interaction between a scalar quantum field φ(x), and many different boundary configurations constructed from (parallel and orthogonal) thin planar surfaces on which φ(x) is constrained to vanish, or to satisfy Neumann conditions. For most of these boundaries the Casimir problem has not previously been investigated. We calculate the canonical and improved vacuum stress tensors left angle T μv (x) right angle and left angle direct difference μv (x) right angle of φ(x) for each example. From these we obtain the local Casimir forces on all boundary planes. For massless fields, both vacuum stress tensors yield identical attractive local Casimir forces in all Dirichlet examples considered. This desirable outcome is not a priori obvious, given the quite different features of left angle T μv (x) right angle and left angle direct difference μv (x) right angle. For Neumann conditions, left angle T μv (x) right angle and left angle direct difference μv (x) right angle lead to attractive Casimir stresses which are not always the same. We also consider Dirichlet and Neumann boundaries immersed in a common scalar quantum field, and find that these repel. The extensive catalogue of worked examples presented here belongs to a large class of completely solvable Casimir problems. Casimir forces previously unknown are predicted, among them ones which might be measurable. (orig.)

  4. Bilinear covariants and spinor fields duality in quantum Clifford algebras

    Energy Technology Data Exchange (ETDEWEB)

    Abłamowicz, Rafał, E-mail: rablamowicz@tntech.edu [Department of Mathematics, Box 5054, Tennessee Technological University, Cookeville, Tennessee 38505 (United States); Gonçalves, Icaro, E-mail: icaro.goncalves@ufabc.edu.br [Instituto de Matemática e Estatística, Universidade de São Paulo, Rua do Matão, 1010, 05508-090, São Paulo, SP (Brazil); Centro de Matemática, Computação e Cognição, Universidade Federal do ABC, 09210-170 Santo André, SP (Brazil); Rocha, Roldão da, E-mail: roldao.rocha@ufabc.edu.br [Centro de Matemática, Computação e Cognição, Universidade Federal do ABC, 09210-170 Santo André, SP (Brazil); International School for Advanced Studies (SISSA), Via Bonomea 265, 34136 Trieste (Italy)

    2014-10-15

    Classification of quantum spinor fields according to quantum bilinear covariants is introduced in a context of quantum Clifford algebras on Minkowski spacetime. Once the bilinear covariants are expressed in terms of algebraic spinor fields, the duality between spinor and quantum spinor fields can be discussed. Thus, by endowing the underlying spacetime with an arbitrary bilinear form with an antisymmetric part in addition to a symmetric spacetime metric, quantum algebraic spinor fields and deformed bilinear covariants can be constructed. They are thus compared to the classical (non quantum) ones. Classes of quantum spinor fields classes are introduced and compared with Lounesto's spinor field classification. A physical interpretation of the deformed parts and the underlying Z-grading is proposed. The existence of an arbitrary bilinear form endowing the spacetime already has been explored in the literature in the context of quantum gravity [S. W. Hawking, “The unpredictability of quantum gravity,” Commun. Math. Phys. 87, 395 (1982)]. Here, it is shown further to play a prominent role in the structure of Dirac, Weyl, and Majorana spinor fields, besides the most general flagpoles and flag-dipoles. We introduce a new duality between the standard and the quantum spinor fields, by showing that when Clifford algebras over vector spaces endowed with an arbitrary bilinear form are taken into account, a mixture among the classes does occur. Consequently, novel features regarding the spinor fields can be derived.

  5. Relativistic quantum information in detectors–field interactions

    International Nuclear Information System (INIS)

    Hu, B L; Lin, Shih-Yuin; Louko, Jorma

    2012-01-01

    We review Unruh–DeWitt detectors and other models of detector–field interaction in a relativistic quantum field theory setting as a tool for extracting detector–detector, field–field and detector–field correlation functions of interest in quantum information science, from entanglement dynamics to quantum teleportation. In particular, we highlight the contrast between the results obtained from linear perturbation theory which can be justified provided switching effects are properly accounted for, and the nonperturbative effects from available analytic expressions which incorporate the backreaction effects of the quantum field on the detector behavior. (paper)

  6. Dressed photons in a new paradigm of off-shell quantum fields

    Science.gov (United States)

    Sakuma, Hirofumi; Ojima, Izumi; Ohtsu, Motoichi

    2017-09-01

    This article reviews recent progress in theoretical studies of dressed photons. For providing concrete physical images of dressed photons, several experimental studies are demonstrated. They are applications of dressed photons to novel optical functional devices, nano-fabrication technologies, energy conversion technologies, and photon breeding devices. After these experimental demonstrations, as the main part of this review, quantum-field theoretical formulation of dressed photons is attempted in use of the newly introduced Clebsch-dual variable of electromagnetic field. The reason for introducing the new formulation will be explained in the final section from the viewpoint to exhibit the contrast between free and interacting quantum fields in regard to their energy-momentum supports which are seldom touched upon (or forgotten) in the common physical discussions about quantum fields.

  7. A Field-Theoretic Approach to the Wiener Sausage

    Science.gov (United States)

    Nekovar, S.; Pruessner, G.

    2016-05-01

    The Wiener Sausage, the volume traced out by a sphere attached to a Brownian particle, is a classical problem in statistics and mathematical physics. Initially motivated by a range of field-theoretic, technical questions, we present a single loop renormalised perturbation theory of a stochastic process closely related to the Wiener Sausage, which, however, proves to be exact for the exponents and some amplitudes. The field-theoretic approach is particularly elegant and very enjoyable to see at work on such a classic problem. While we recover a number of known, classical results, the field-theoretic techniques deployed provide a particularly versatile framework, which allows easy calculation with different boundary conditions even of higher momenta and more complicated correlation functions. At the same time, we provide a highly instructive, non-trivial example for some of the technical particularities of the field-theoretic description of stochastic processes, such as excluded volume, lack of translational invariance and immobile particles. The aim of the present work is not to improve upon the well-established results for the Wiener Sausage, but to provide a field-theoretic approach to it, in order to gain a better understanding of the field-theoretic obstacles to overcome.

  8. Theoretical/Computational Studies of High-Temperature Superconductivity from Quantum Magnetism

    Science.gov (United States)

    2016-06-09

    AFRL-AFOSR-VA-TR-2016-0204 Theoretical/Computational Studies of High-Temperature Superconductivity from Quantum Magnetism Jose Rodriguez CALIFORNIA...TITLE AND SUBTITLE Theoretical/Computational Studies of High-Temperature Superconductivity from Quantum Magnetism 5a.  CONTRACT NUMBER 5b.  GRANT...SUBJECT TERMS quantum magnetism , HTS, superconductivity 16.  SECURITY CLASSIFICATION OF: 17.  LIMITATION OF       ABSTRACT UU 18.  NUMBER        OF

  9. Integrable models in 1+1 dimensional quantum field theory

    International Nuclear Information System (INIS)

    Faddeev, Ludvig.

    1982-09-01

    The goal of this lecture is to present a unifying view on the exactly soluble models. There exist several reasons arguing in favor of the 1+1 dimensional models: every exact solution of a field-theoretical model can teach about the ability of quantum field theory to describe spectrum and scattering; some 1+1 d models have physical applications in the solid state theory. There are several ways to become acquainted with the methods of exactly soluble models: via classical statistical mechanics, via Bethe Ansatz, via inverse scattering method. Fundamental Poisson bracket relation FPR and/or fundamental commutation relations FCR play fundamental role. General classification of FPR is given with promizing generalizations to FCR

  10. Quantum field theory and critical phenomena

    CERN Document Server

    Zinn-Justin, Jean

    1996-01-01

    Over the last twenty years quantum field theory has become not only the framework for the discussion of all fundamental interactions except gravity, but also for the understanding of second-order phase transitions in statistical mechanics. This advanced text is based on graduate courses and summer schools given by the author over a number of years. It approaches the subject in terms of path and functional intergrals, adopting a Euclidean metric and using the language of partition and correlation functions. Renormalization and the renormalization group are examined, as are critical phenomena and the role of instantons. Changes for this edition 1. Extensive revision to eliminate a few bugs that had survived the second edition and (mainly) to improve the pedagogical presentation, as a result of experience gathered by lecturing. 2. Additional new topics; holomorphic or coherent state path integral; functional integral and representation of the field theory S-matrix in the holomorphic formalis; non-relativistic li...

  11. The pure phases, the irreducible quantum fields, and dynamical symmetry breaking in Symanzik--Nelson positive quantum field theories

    International Nuclear Information System (INIS)

    Frohlich, J.

    1976-01-01

    We prove that a Symanzik--Nelson positive quantum field theory, i.e., a quantum field theory derived from a Euclidean field theory, has a unique decomposition into pure phases which preserves Symanzik--Nelson positivity and Poincare covariance. We derive useful sufficient conditions for the breakdown of an internal symmetry of such a theory in its pure phases, for the self-adjointness and nontrivially (in the sense of Borchers classes) of its quantum fields, and the existence of time-ordered and retarded products. All these general results are then applied to the P (phi) 2 and the phi 3 4 quantum field models

  12. Quantum field theory of point particles and strings

    CERN Document Server

    Hatfield, Brian

    1992-01-01

    The purpose of this book is to introduce string theory without assuming any background in quantum field theory. Part I of this book follows the development of quantum field theory for point particles, while Part II introduces strings. All of the tools and concepts that are needed to quantize strings are developed first for point particles. Thus, Part I presents the main framework of quantum field theory and provides for a coherent development of the generalization and application of quantum field theory for point particles to strings.Part II emphasizes the quantization of the bosonic string.

  13. Quantum Field Thoery at the Limits

    CERN Document Server

    2016-01-01

    The Helmholtz International Summer School (HISS) - Dubna International Advanced School of Theoretical Physics (DIAS-TH) "Physics of Heavy Quarks and Hadrons", organized by the Bogoliubov Laboratory of Theoretical Physics of the Joint Institute for Nuclear Research, will be held from 18 to 30 July, 2016 in Dubna. It continues a series of workshops and schools held in Dubna (1993, 1996, 2000, 2002, 2005, 2008, 2013) and Bad Honnef (1994) and Rostock (1997). The School will cover the main topics in heavy flavor physics. It will provide a first hand opportunity to a good number of graduate students and postdocs in high energy physics to hear the latest results on heavy quark physics from all four experimental collaborations at the LHC (ATLAS, CMS, LHCb, ALICE) and from the B-factory at the KEK. Leading experts in this field will read a series of lectures devoted to theoretical analysis of the experimental results. Some lectures will be devoted to strong-field QED and high-intensity plasma physics. The lecture...

  14. Electromagnetic fields on a quantum scale. I.

    Science.gov (United States)

    Grimes, Dale M; Grimes, Craig A

    2002-10-01

    This is the first in a series of two articles, the second of which provides an exact electro-magnetic field description of photon emission, absorption, and radiation pattern. Photon energy exchanges are analyzed and shown to be the triggered, regenerative response of a non-local eigenstate electron. This first article presents a model-based, hidden variable analysis of quantum theory that provides the statistical nature of wave functions. The analysis uses the equations of classical electro-magnetism and conservation of energy while modeling an eigenstate electron as a nonlocal entity. Essential to the analysis are physical properties that were discovered and analyzed only after the historical interpretation of quantum mechanics was established: electron non-locality and the standing electro-magnetic energy that accompanies and encompasses an active, electrically small volume. The standing energy produces a driving radiation reaction force that, under certain circumstances, is many orders of magnitude larger than currently accepted values. These properties provide a sufficient basis for the Schrödinger equation as a descriptor of non-relativistic eigenstate electrons in or near equilibrium. The uncertainty principle follows, as does the exclusion principle. The analysis leads to atomic stability and causality in the sense that the status of physical phenomena at any instant specifies the status an instant later.

  15. Effective and fundamental quantum fields at criticality

    Energy Technology Data Exchange (ETDEWEB)

    Scherer, Michael

    2010-10-28

    We employ Wetterich's approach to functional renormalization as a suitable method to investigate universal phenomena in non-perturbative quantum field theories both qualitatively and quantitatively. Therefore we derive and investigate flow equations for a class of chiral Yukawa models with and without gauge bosons and reveal fixed-point mechanisms. In four dimensions chiral Yukawa systems serve as toy models for the standard model Higgs sector and show signatures of asymptotically safe fixed points by a balancing of bosonic and fermionic contributions. In the approximations investigated this renders the theory fundamental and solves the triviality problem. Further, we obtain predictions for the Higgs mass and even for the top mass of our toy model. In three dimensions we compute the critical exponents which define new universality classes and provide benchmark values for systems of strongly correlated chiral fermions. In a Yukawa system of non-relativistic two-component fermions a fixed point dominates the renormalization flow giving rise to universality in the BCS-BEC crossover. We push the functional renormalization method to a quantitative level and we compute the critical temperature and the single-particle gap with a considerable precision for the whole crossover. Finally, we provide further evidence for the asymptotic safety scenario in quantum gravity by confirming the existence of an ultraviolet fixed point under inclusion of a curvature-ghost coupling. (orig.)

  16. Protected gates for topological quantum field theories

    Science.gov (United States)

    Beverland, Michael E.; Buerschaper, Oliver; Koenig, Robert; Pastawski, Fernando; Preskill, John; Sijher, Sumit

    2016-02-01

    We study restrictions on locality-preserving unitary logical gates for topological quantum codes in two spatial dimensions. A locality-preserving operation is one which maps local operators to local operators — for example, a constant-depth quantum circuit of geometrically local gates, or evolution for a constant time governed by a geometrically local bounded-strength Hamiltonian. Locality-preserving logical gates of topological codes are intrinsically fault tolerant because spatially localized errors remain localized, and hence sufficiently dilute errors remain correctable. By invoking general properties of two-dimensional topological field theories, we find that the locality-preserving logical gates are severely limited for codes which admit non-abelian anyons, in particular, there are no locality-preserving logical gates on the torus or the sphere with M punctures if the braiding of anyons is computationally universal. Furthermore, for Ising anyons on the M-punctured sphere, locality-preserving gates must be elements of the logical Pauli group. We derive these results by relating logical gates of a topological code to automorphisms of the Verlinde algebra of the corresponding anyon model, and by requiring the logical gates to be compatible with basis changes in the logical Hilbert space arising from local F-moves and the mapping class group.

  17. Protected gates for topological quantum field theories

    Energy Technology Data Exchange (ETDEWEB)

    Beverland, Michael E.; Pastawski, Fernando; Preskill, John [Institute for Quantum Information and Matter, California Institute of Technology, Pasadena, California 91125 (United States); Buerschaper, Oliver [Dahlem Center for Complex Quantum Systems, Freie Universität Berlin, 14195 Berlin (Germany); Koenig, Robert [Institute for Advanced Study and Zentrum Mathematik, Technische Universität München, 85748 Garching (Germany); Sijher, Sumit [Institute for Quantum Computing and Department of Applied Mathematics, University of Waterloo, Waterloo, Ontario N2L 3G1 (Canada)

    2016-02-15

    We study restrictions on locality-preserving unitary logical gates for topological quantum codes in two spatial dimensions. A locality-preserving operation is one which maps local operators to local operators — for example, a constant-depth quantum circuit of geometrically local gates, or evolution for a constant time governed by a geometrically local bounded-strength Hamiltonian. Locality-preserving logical gates of topological codes are intrinsically fault tolerant because spatially localized errors remain localized, and hence sufficiently dilute errors remain correctable. By invoking general properties of two-dimensional topological field theories, we find that the locality-preserving logical gates are severely limited for codes which admit non-abelian anyons, in particular, there are no locality-preserving logical gates on the torus or the sphere with M punctures if the braiding of anyons is computationally universal. Furthermore, for Ising anyons on the M-punctured sphere, locality-preserving gates must be elements of the logical Pauli group. We derive these results by relating logical gates of a topological code to automorphisms of the Verlinde algebra of the corresponding anyon model, and by requiring the logical gates to be compatible with basis changes in the logical Hilbert space arising from local F-moves and the mapping class group.

  18. Open-System Quantum Annealing in Mean-Field Models with Exponential Degeneracy*

    Directory of Open Access Journals (Sweden)

    Kostyantyn Kechedzhi

    2016-05-01

    Full Text Available Real-life quantum computers are inevitably affected by intrinsic noise resulting in dissipative nonunitary dynamics realized by these devices. We consider an open-system quantum annealing algorithm optimized for such a realistic analog quantum device which takes advantage of noise-induced thermalization and relies on incoherent quantum tunneling at finite temperature. We theoretically analyze the performance of this algorithm considering a p-spin model that allows for a mean-field quasiclassical solution and, at the same time, demonstrates the first-order phase transition and exponential degeneracy of states, typical characteristics of spin glasses. We demonstrate that finite-temperature effects introduced by the noise are particularly important for the dynamics in the presence of the exponential degeneracy of metastable states. We determine the optimal regime of the open-system quantum annealing algorithm for this model and find that it can outperform simulated annealing in a range of parameters. Large-scale multiqubit quantum tunneling is instrumental for the quantum speedup in this model, which is possible because of the unusual nonmonotonous temperature dependence of the quantum-tunneling action in this model, where the most efficient transition rate corresponds to zero temperature. This model calculation is the first analytically tractable example where open-system quantum annealing algorithm outperforms simulated annealing, which can, in principle, be realized using an analog quantum computer.

  19. Quantum group structure and local fields in the algebraic approach to 2D gravity

    CERN Document Server

    Schnittger, Jens

    1994-01-01

    This review contains a summary of work by J.-L. Gervais and the author on the operator approach to 2d gravity. Special emphasis is placed on the construction of local observables -the Liouville exponentials and the Liouville field itself - and the underlying algebra of chiral vertex operators. The double quantum group structure arising from the presence of two screening charges is discussed and the generalized algebra and field operators are derived. In the last part, we show that our construction gives rise to a natural definition of a quantum tau function, which is a noncommutative version of the classical group-theoretic representation of the Liouville fields by Leznov and Saveliev.

  20. Quantum field theory treatment of magnetic effects on a system of free electrons

    Science.gov (United States)

    Verzegnassi, C.; Germano, R.; Kurian, P.

    2018-03-01

    The effects of a magnetic field on the energy and on the spin of free electrons are computed in the theoretical framework of quantum field theory. In the case of a static moderate field and with relatively slow electrons, the derived formulae are particularly simple. A comparison with the approaches of classical physics and of quantum mechanics shows essential differences and important analogies. The relevance to the magnetic effects of the initial polarization components of the electron states and the possible existence of special values of these quantities are discussed in the final conclusions, which might be useful to explain recent experiments on quasi-free electrons in chiral systems in biology.

  1. Temporal description of thermal quantum fields

    International Nuclear Information System (INIS)

    Umezawa, H.; Yamanaka, Y.

    1992-01-01

    In this paper, making use of time-dependent Bogoliubov transformations, the authors develop a calculation technique for time-dependent non-equilibrium systems of quantum fields in a time-representation (t-representation). The corrected one-body propagator in the t-representation turns out to have the form B - 1 (diagonal matrix) B (B being a thermal Bogoliubov matrix). Applying the usual on-shell concept to the diagonal matrix part of the self-energy, we formulate a self-consistent renormalization scheme. This renormalization determines the vacuum and leads to a kinetic equation for the number density parameter, which reduces to the Boltzmann equation in the lowest approximation. This gives the authors the increasing entropy in time (the second law of thermodynamics)

  2. Quantum phase transition of the transverse-field quantum Ising model on scale-free networks.

    Science.gov (United States)

    Yi, Hangmo

    2015-01-01

    I investigate the quantum phase transition of the transverse-field quantum Ising model in which nearest neighbors are defined according to the connectivity of scale-free networks. Using a continuous-time quantum Monte Carlo simulation method and the finite-size scaling analysis, I identify the quantum critical point and study its scaling characteristics. For the degree exponent λ=6, I obtain results that are consistent with the mean-field theory. For λ=4.5 and 4, however, the results suggest that the quantum critical point belongs to a non-mean-field universality class. Further simulations indicate that the quantum critical point remains mean-field-like if λ>5, but it continuously deviates from the mean-field theory as λ becomes smaller.

  3. Spin-Orbit Coupling, Antilocalization, and Parallel Magnetic Fields in Quantum Dots

    DEFF Research Database (Denmark)

    Zumbuhl, D.; Miller, Jessica; M. Marcus, C.

    2002-01-01

    We investigate antilocalization due to spin-orbit coupling in ballistic GaAs quantum dots. Antilocalization that is prominent in large dots is suppressed in small dots, as anticipated theoretically. Parallel magnetic fields suppress both antilocalization and also, at larger fields, weak...... localization, consistent with random matrix theory results once orbital coupling of the parallel field is included. In situ control of spin-orbit coupling in dots is demonstrated as a gate-controlled crossover from weak localization to antilocalization....

  4. Geophysical field disturbances and quantum mechanics

    Directory of Open Access Journals (Sweden)

    Kuznetsov Vladimir

    2017-01-01

    Geophysical phenomena considered here have no clear and consistent interpretation in the context of classical physics. We attempt to involve the recent achievements of quantum physics namely the quantum entanglement between elementary particles implicated in considered phenomena.

  5. Excitons and trions in single and vertically coupled quantum dots under an electric field

    Science.gov (United States)

    Zhai, Li-Xue; Wang, Yan; An, Zhong

    2017-08-01

    We present a theoretical study of the exciton (X0), the positive and negative trions (X+ and X-) in single and vertically coupled configurations of self-assembled InGaAs quantum dots under an electric field. The quantum states of X0, X+ and X- have been investigated using a quasi-one-dimensional (Q1D) model within the effective-mass approximation. For the single quantum dots, the electric-field dependent energy levels and the average inter-particle distances for the exciton and trions have been calculated. For the coupled quantum dots, the ground and the excited states for X0, X+ and X- have also been calculated and discussed. It is found that either the hole or the electron can be tuned into resonance states by the electric field and that the transition energy spectra for both trions consequently show crossing and anticrossing patterns. The recombination probabilities of the exciton and trion optical transitions are also calculated. The theoretical results have been compared with previously reported photoluminescence data and qualitative agreement is obtained. The trion conditional wave functions are also plotted under different electric field intensities, and it is found that a molecular orbital can be formed at a critical electric field intensity. The evolution of the energy levels of the trions in coupled quantum dots can be explained by the interplay of particle transfer and the electric field.

  6. Mid-Infrared Quantum-Dot Quantum Cascade Laser: A Theoretical Feasibility Study

    Directory of Open Access Journals (Sweden)

    Stephan Michael

    2016-05-01

    Full Text Available In the framework of a microscopic model for intersubband gain from electrically pumped quantum-dot structures we investigate electrically pumped quantum-dots as active material for a mid-infrared quantum cascade laser. Our previous calculations have indicated that these structures could operate with reduced threshold current densities while also achieving a modal gain comparable to that of quantum well active materials. Here, we study the influence of two important quantum-dot material parameters, namely inhomogeneous broadening and quantum-dot sheet density, on the performance of a proposed quantum cascade laser design. In terms of achieving a positive modal net gain, a high quantum-dot density can compensate for moderately high inhomogeneous broadening, but at a cost of increased threshold current density. However, by minimizing quantum-dot density with presently achievable inhomogeneous broadening and total losses, significantly lower threshold densities than those reported in quantum-well quantum-cascade lasers are predicted by our theory.

  7. Quantum trajectory in a time-dependent potential : oscillator in a monochromatic field

    OpenAIRE

    Nishiyama, Yoshio

    2002-01-01

    The 'quantum trajectory' obeying the Schrodinger equation with a time dependent potential is theoretically determined. As an illustration of the theory the trajectory of a charged harmonic oscillator in an electromagnetic field obeying the wave equation is shown along with the orbital motion of the corresponding classical particle.

  8. Quantum theoretical study of hydrogen under high pressure

    International Nuclear Information System (INIS)

    Biermann, S.

    2001-12-01

    In the first chapter we will review our knowledge of the phase diagram of hydrogen. Chapter 2 is dedicated to a summary of the standard density functional and molecular dynamics methods and shows how these are combined in the Car-Parrinello method. Here the nuclei are still treated as classical particles obeying Newtonian mechanics. In chapter 3 we drop this approximation. The path integral description of quantum statistics is added on top of the classical Car-Parrinello method and yields a formalism that includes quantum effects due to the finite de Broglie wavelength of the nuclei. Some technical aspects, namely the parallel implementation of the Path Integral Car-Parrinello (PICP) method, are discussed in chapter 4. In chapter 5 we present the results of our PICP calculations and compare them with prior calculations using the classical Car-Parrinello method as described in chapter 2. (orig.)

  9. Extension of PT-symmetric quantum mechanics to quantum field theory with cubic interaction

    International Nuclear Information System (INIS)

    Bender, Carl M.; Brody, Dorje C.; Jones, Hugh F.

    2004-01-01

    It has recently been shown that a non-Hermitian Hamiltonian H possessing an unbroken PT symmetry (i) has a real spectrum that is bounded below, and (ii) defines a unitary theory of quantum mechanics with positive norm. The proof of unitarity requires a linear operator C, which was originally defined as a sum over the eigenfunctions of H. However, using this definition to calculate C is cumbersome in quantum mechanics and impossible in quantum field theory. An alternative method is devised here for calculating C directly in terms of the operator dynamical variables of the quantum theory. This method is general and applies to a variety of quantum mechanical systems having several degrees of freedom. More importantly, this method is used to calculate the C operator in quantum field theory. The C operator is a time-independent observable in PT-symmetric quantum field theory

  10. Thermal quantum discord of spins in an inhomogeneous magnetic field

    International Nuclear Information System (INIS)

    Guo Jinliang; Mi Yingjuan; Zhang Jian; Song Heshan

    2011-01-01

    In contrast with the thermal entanglement, we study the quantum discord and classical correlation in a two-qubit Heisenberg XXZ model with an inhomogeneous magnetic field. It is shown that the effects of the external magnetic fields, including the uniform and inhomogeneous magnetic fields, on the thermal entanglement, quantum discord and classical correlation behave differently in various aspects, which depend on system temperature and model type. We can tune the inhomogeneous magnetic field to enhance the entanglement or classical correlation and meanwhile decrease the quantum discord. In addition, taking into account the inhomogeneous magnetic field, the sudden change in the behaviour of quantum discord still survives, which can detect the critical points of quantum phase transitions at finite temperature, but not for a uniform magnetic field.

  11. Quantum tunneling and field electron emission theories

    CERN Document Server

    Liang, Shi-Dong

    2013-01-01

    Quantum tunneling is an essential issue in quantum physics. Especially, the rapid development of nanotechnology in recent years promises a lot of applications in condensed matter physics, surface science and nanodevices, which are growing interests in fundamental issues, computational techniques and potential applications of quantum tunneling. The book involves two relevant topics. One is quantum tunneling theory in condensed matter physics, including the basic concepts and methods, especially for recent developments in mesoscopic physics and computational formulation. The second part is the f

  12. A quantum theoretical approach to information processing in neural networks

    Science.gov (United States)

    Barahona da Fonseca, José; Barahona da Fonseca, Isabel; Suarez Araujo, Carmen Paz; Simões da Fonseca, José

    2000-05-01

    A reinterpretation of experimental data on learning was used to formulate a law on data acquisition similar to the Hamiltonian of a mechanical system. A matrix of costs in decision making specifies values attributable to a barrier that opposed to hypothesis formation about decision making. The interpretation of the encoding costs as frequencies of oscillatory phenomena leads to a quantum paradigm based in the models of photoelectric effect as well as of a particle against a potential barrier. Cognitive processes are envisaged as complex phenomena represented by structures linked by valence bounds. This metaphor is used to find some prerequisites to certain types of conscious experience as well as to find an explanation for some pathological distortions of cognitive operations as they are represented in the context of the isolobal model. Those quantum phenomena are understood as representing an analogue programming for specific special purpose computations. The formation of complex chemical structures within the context of isolobal theory is understood as an analog quantum paradigm for complex cognitive computations.

  13. Lectures on algebraic quantum field theory and operator algebras

    International Nuclear Information System (INIS)

    Schroer, Bert

    2001-04-01

    In this series of lectures directed towards a mainly mathematically oriented audience I try to motivate the use of operator algebra methods in quantum field theory. Therefore a title as why mathematicians are/should be interested in algebraic quantum field theory would be equally fitting. besides a presentation of the framework and the main results of local quantum physics these notes may serve as a guide to frontier research problems in mathematical. (author)

  14. The polarization response in InAs quantum dots: theoretical correlation between composition and electronic properties

    International Nuclear Information System (INIS)

    Usman, Muhammad; O’Reilly, Eoin P; Tasco, Vittorianna; Todaro, Maria Teresa; De Giorgi, Milena; Passaseo, Adriana; Klimeck, Gerhard

    2012-01-01

    III–V growth and surface conditions strongly influence the physical structure and resulting optical properties of self-assembled quantum dots (QDs). Beyond the design of a desired active optical wavelength, the polarization response of QDs is of particular interest for optical communications and quantum information science. Previous theoretical studies based on a pure InAs QD model failed to reproduce experimentally observed polarization properties. In this work, multi-million atom simulations are performed in an effort to understand the correlation between chemical composition and polarization properties of QDs. A systematic analysis of QD structural parameters leads us to propose a two-layer composition model, mimicking In segregation and In–Ga intermixing effects. This model, consistent with mostly accepted compositional findings, allows us to accurately fit the experimental PL spectra. The detailed study of QD morphology parameters presented here serves as a tool for using growth dynamics to engineer the strain field inside and around the QD structures, allowing tuning of the polarization response. (paper)

  15. Theoretical Femtosecond Physics Atoms and Molecules in Strong Laser Fields

    CERN Document Server

    Grossmann, Frank

    2008-01-01

    Theoretical femtosecond physics is a new field of research. Theoretical investigations of atoms and molecules interacting with pulsed or continuous wave lasers of up to atomic field strengths are leading to an understanding of many challenging experimental discoveries. Laser-matter interaction is treated on a nonperturbative level in the book using approximate and numerical solutions of the time-dependent Schrödinger equation. The light field is treated classically. Physical phenomena, ranging from ionization of atoms to the ionization and dissociation of molecules and the control of chemical reactions are presented and discussed. Theoretical background for experiments with strong and short laser pulses is given. Several exercises are included in the main text. Some detailed calculations are performed in the appendices.

  16. Quantum field theory and the internal states of elementary particles

    CSIR Research Space (South Africa)

    Greben, JM

    2011-01-01

    Full Text Available satisfying coupled quantum field equations, all expressed at the same space-time coordinate. Quantization is realized by expanding the quantum fields in terms of fermionic creation and annihilation operators. This approach is applied in a QCD description...

  17. Classical Solutions in Quantum Field Theory

    International Nuclear Information System (INIS)

    Mann, Robert

    2013-01-01

    Quantum field theory has evolved from its early beginnings as a tool for understanding the interaction of light with matter into a rather formidable technical paradigm, one that has successfully provided the mathematical underpinnings of all non-gravitational interactions. Over the eight decades since it was first contemplated the methods have become increasingly more streamlined and sophisticated, yielding new insights into our understanding of the subatomic world and our abilities to make clear and precise predictions. Some of the more elegant methods have to do with non-perturbative and semiclassical approaches to the subject. The chief players here are solitons, instantons, and anomalies. Over the past three decades there has been a steady rise in our understanding of these objects and of our ability to calculate their effects and implications for the rest of quantum field theory. This book is a welcome contribution to this subject. In 12 chapters it provides a clear synthesis of the key developments in these subjects at a level accessible to graduate students that have had an introductory course to quantum field theory. In the author's own words it provides both 'a survey and an overview of this field'. The first half of the book concentrates on solitons-–kinks, vortices, and magnetic monopoles-–and their implications for the subject. The reader is led first through the simplest models in one spatial dimension, into more sophisticated cases that required more advanced topological methods. The author does quite a nice job of introducing the various concepts as required, and beginning students should be able to get a good grasp of the subject directly from the text without having to first go through the primary literature. The middle part of the book deals with the implications of these solitons for both cosmology and for duality. While the cosmological discussion is quite nice, the discussion on BPS solitons, supersymmetry and duality is

  18. Double Exponential Relativity Theory Coupled Theoretically with Quantum Theory?

    International Nuclear Information System (INIS)

    Montero Garcia, Jose de la Luz; Novoa Blanco, Jesus Francisco

    2007-01-01

    Here the problem of special relativity is analyzed into the context of a new theoretical formulation: the Double Exponential Theory of Special Relativity with respect to which the current Special or Restricted Theory of Relativity (STR) turns to be a particular case only

  19. Information-theoretic treatment of tripartite systems and quantum channels

    International Nuclear Information System (INIS)

    Coles, Patrick J.; Yu Li; Gheorghiu, Vlad; Griffiths, Robert B.

    2011-01-01

    A Holevo measure is used to discuss how much information about a given positive operator valued measure (POVM) on system a is present in another system b, and how this influences the presence or absence of information about a different POVM on a in a third system c. The main goal is to extend information theorems for mutually unbiased bases or general bases to arbitrary POVMs, and especially to generalize ''all-or-nothing'' theorems about information located in tripartite systems to the case of partial information, in the form of quantitative inequalities. Some of the inequalities can be viewed as entropic uncertainty relations that apply in the presence of quantum side information, as in recent work by Berta et al. [Nature Physics 6, 659 (2010)]. All of the results also apply to quantum channels: For example, if E accurately transmits certain POVMs, the complementary channel F will necessarily be noisy for certain other POVMs. While the inequalities are valid for mixed states of tripartite systems, restricting to pure states leads to the basis invariance of the difference between the information about a contained in b and c.

  20. Bookshelf (An Introduction to Quantum field theory, by G. Sterman)

    International Nuclear Information System (INIS)

    Nason, Paolo

    1994-01-01

    This book contains a systematic presentation of quantum field theory. Canonical quantization, path integrals, non-abelian gauge theories, renormalization and axial anomalies are discussed to a satisfactory level, so that the book can be easily used for an introductory course in field theory. The most interesting aspect of the book is contained in Part IV, with a full treatment of soft and collinear singularities, together with a discussion of the meaning of perturbative cross-sections when soft and infrared divergences are present. This subject is too often neglected in textbooks, in spite of the fact that a large amount of current research in high energy physics (and much of the motivation for QCD as a theory for strong interactions) is based on it. The author is certainly a great expert in this field, to which he has brought many important contributions. The core of Part IV is a demonstration of the infrared finiteness of jet crosssections in electron-positron annihilation. Following this, the more complex topic of hadron-initiated reactions involving hadrons in the initial state is dealt with. The physics of scaling violation in both the parton model and in terms of the operator product expansion is discussed. The computation of first order corrections to deep inelastic scattering and to the Drell-Yan pair production process, which marks the beginning of the application of perturbative QCD to hadronic collisions, is given in detail, illustrating the factorization of the hadronic cross-section into a short distance cross-section and a universal parton density. One apparent limitation of the book is its lack of explicit contact with phenomenology. Comparison of theoretical calculations with experimental results are never mentioned (the only graphs one finds in the book are Feynman graphs). The book is therefore mainly aimed at theoretical physicists. However field theory courses are generally paralleled or followed by a course in particle physics phenomenology

  1. Near-field optical spectroscopy of single quantum wires

    Science.gov (United States)

    Harris, T. D.; Gershoni, D.; Grober, R. D.; Pfeiffer, L.; West, K.; Chand, N.

    1996-02-01

    Low temperature near-field scanning optical microscopy is used for spectroscopic studies of single, nanometer dimension, cleaved edge overgrown quantum wires. A direct experimental comparison between a two dimensional system and a single genuinely one dimensional quantum wire system, inaccessible to conventional far field optical spectroscopy, is enabled by the enhanced spatial resolution. We show that the photoluminescence of a single quantum wire is easily distinguished from that of the surrounding quantum well. Emission from localized centers is shown to dominate the photoluminescence from both wires and wells at low temperatures. A factor of 3 absorption enhancement for these wires compared to the wells is concluded from the photoluminescence excitation data.

  2. Einstein and interpretation of quantum field theory

    International Nuclear Information System (INIS)

    Kashlyun, F.

    1982-01-01

    The main problems of the quantum theory, the basis of which was laid by Planck in 1900 as a result of the discovery of elementary quantum of action, are examined. The most important Einstein contributions to the quantum theory are enumerated. The Einstein work about the light quanta, proved wave-particle dualism, stated one of the most complicated problems to the physics. The work on the specific heat capacity of solids shows that the quantum theory should be beyond the limits of the narrow range of the problems on black radiation. The works on the equilibrium of radiation have convincingly demonstrates statistical character of the radiation processes and have marked the way to Heizenberg form of the quantum mechanics. Einstein generalized the idea of wave-particle dualism to the ordinary gas. It helped to prepare the Schroedinger form of quantum mechanics

  3. Algebraic quantum field theory, perturbation theory, and the loop expansion

    International Nuclear Information System (INIS)

    Duetsch, M.; Fredenhagen, K.

    2001-01-01

    The perturbative treatment of quantum field theory is formulated within the framework of algebraic quantum field theory. We show that the algebra of interacting fields is additive, i.e. fully determined by its subalgebras associated to arbitrary small subregions of Minkowski space. We also give an algebraic formulation of the loop expansion by introducing a projective system A (n) of observables ''up to n loops'', where A (0) is the Poisson algebra of the classical field theory. Finally we give a local algebraic formulation for two cases of the quantum action principle and compare it with the usual formulation in terms of Green's functions. (orig.)

  4. Probing a quantum field in a photon box

    International Nuclear Information System (INIS)

    Raimond, J M; Meunier, T; Bertet, P; Gleyzes, S; Maioli, P; Auffeves, A; Nogues, G; Brune, M; Haroche, S

    2005-01-01

    Einstein often performed thought experiments with 'photon boxes', storing fields for unlimited times. This is yet but a dream. We can nevertheless store quantum microwave fields in superconducting cavities for billions of periods. Using circular Rydberg atoms, it is possible to probe in a very detailed way the quantum state of these trapped fields. Cavity quantum electrodynamics tools can be used for a direct determination of the Husimi Q and Wigner quasi-probability distributions. They provide a very direct insight into the classical or non-classical nature of the field

  5. Field-theoretic calculation of kinetic helicity flux

    Indian Academy of Sciences (India)

    In this paper we apply perturbative field-theoretic technique to helical turbulence. In the inertial range the kinetic helicity flux is found to be constant and forward. The universal constant H appearing in the spectrum of kinetic helicity was found to be 2.47.

  6. The quantum harmonic oscillator on a circle and a deformed quantum field theory

    International Nuclear Information System (INIS)

    Rego-Monteiro, M.A.

    2001-05-01

    We construct a deformed free quantum field theory with an standard Hilbert space based on a deformed Heisenberg algebra. This deformed algebra is a Heisenberg-type algebra describing the first levels of the quantum harmonic oscillator on a circle of large length L. The successive energy levels of this quantum harmonic oscillator on a circle of large length L are interpreted, similarly to the standard quantum one-dimensional harmonic oscillator on an infinite line, as being obtained by the creation of a quantum particle of frequency w at very high energies. (author)

  7. Temperature-Dependent Coercive Field Measured by a Quantum Dot Strain Gauge.

    Science.gov (United States)

    Chen, Yan; Zhang, Yang; Keil, Robert; Zopf, Michael; Ding, Fei; Schmidt, Oliver G

    2017-12-13

    Coercive fields of piezoelectric materials can be strongly influenced by environmental temperature. We investigate this influence using a heterostructure consisting of a single crystal piezoelectric film and a quantum dots containing membrane. Applying electric field leads to a physical deformation of the piezoelectric film, thereby inducing strain in the quantum dots and thus modifying their optical properties. The wavelength of the quantum dot emission shows butterfly-like loops, from which the coercive fields are directly derived. The results suggest that coercive fields at cryogenic temperatures are strongly increased, yielding values several tens of times larger than those at room temperature. We adapt a theoretical model to fit the measured data with very high agreement. Our work provides an efficient framework for predicting the properties of ferroelectric materials and advocating their practical applications, especially at low temperatures.

  8. The Evolution of Quantum Field Theory, From QED to Grand Unification

    CERN Document Server

    Hooft, Gerard 't

    2016-01-01

    In the early 1970s, after a slow start, and lots of hurdles, Quantum Field Theory emerged as the superior doctrine for understanding the interactions between relativistic sub-atomic particles. After the conditions for a relativistic field theoretical model to be renormalizable were established, there were two other developments that quickly accelerated acceptance of this approach: first the Brout-Englert-Higgs mechanism, and then asymptotic freedom. Together, these gave us a complete understanding of the perturbative sector of the theory, enough to give us a detailed picture of what is now usually called the Standard Model. Crucial for this understanding were the strong indications and encouragements provided by numerous experimental findings. Subsequently, non-perturbative features of the quantum field theories were addressed, and the first proposals for completely unified quantum field theories were launched. Since the use of continuous symmetries of all sorts, together with other topics of advanced mathema...

  9. Information-theoretic limitations on approximate quantum cloning and broadcasting

    OpenAIRE

    Lemm, Marius; Wilde, Mark M.

    2016-01-01

    We prove quantitative limitations on any approximate simultaneous cloning or broadcasting of mixed states. The results are based on information-theoretic (entropic) considerations and generalize the well-known no-cloning and no-broadcasting theorems. We also observe and exploit the fact that the universal cloning machine on the symmetric subspace of n qudits and symmetrized partial trace channels are dual to each other. This duality manifests itself both in the algebraic sense of adjointness ...

  10. Structural aspects of Lorentz-violating quantum field theory

    Science.gov (United States)

    Cambiaso, M.; Lehnert, R.; Potting, R.

    2018-01-01

    In the last couple of decades the Standard Model Extension has emerged as a fruitful framework to analyze the empirical and theoretical extent of the validity of cornerstones of modern particle physics, namely, of Special Relativity and of the discrete symmetries C, P and T (or some combinations of these). The Standard Model Extension allows to contrast high-precision experimental tests with posited alterations representing minute Lorentz and/or CPT violations. To date no violation of these symmetry principles has been observed in experiments, mostly prompted by the Standard-Model Extension. From the latter, bounds on the extent of departures from Lorentz and CPT symmetries can be obtained with ever increasing accuracy. These analyses have been mostly focused on tree-level processes. In this presentation I would like to comment on structural aspects of perturbative Lorentz violating quantum field theory. I will show that some insight coming from radiative corrections demands a careful reassessment of perturbation theory. Specifically I will argue that both the standard renormalization procedure as well as the Lehmann-Symanzik-Zimmermann reduction formalism need to be adapted given that the asymptotic single-particle states can receive quantum corrections from Lorentz-violating operators that are not present in the original Lagrangian.

  11. Comparison of holographic and field theoretic complexities for time dependent thermofield double states

    Science.gov (United States)

    Yang, Run-Qiu; Niu, Chao; Zhang, Cheng-Yong; Kim, Keun-Young

    2018-02-01

    We compute the time-dependent complexity of the thermofield double states by four different proposals: two holographic proposals based on the "complexity-action" (CA) conjecture and "complexity-volume" (CV) conjecture, and two quantum field theoretic proposals based on the Fubini-Study metric (FS) and Finsler geometry (FG). We find that four different proposals yield both similarities and differences, which will be useful to deepen our understanding on the complexity and sharpen its definition. In particular, at early time the complexity linearly increase in the CV and FG proposals, linearly decreases in the FS proposal, and does not change in the CA proposal. In the late time limit, the CA, CV and FG proposals all show that the growth rate is 2 E/(πℏ) saturating the Lloyd's bound, while the FS proposal shows the growth rate is zero. It seems that the holographic CV conjecture and the field theoretic FG method are more correlated.

  12. Near-field strong coupling of single quantum dots.

    Science.gov (United States)

    Groß, Heiko; Hamm, Joachim M; Tufarelli, Tommaso; Hess, Ortwin; Hecht, Bert

    2018-03-01

    Strong coupling and the resultant mixing of light and matter states is an important asset for future quantum technologies. We demonstrate deterministic room temperature strong coupling of a mesoscopic colloidal quantum dot to a plasmonic nanoresonator at the apex of a scanning probe. Enormous Rabi splittings of up to 110 meV are accomplished by nanometer-precise positioning of the quantum dot with respect to the nanoresonator probe. We find that, in addition to a small mode volume of the nanoresonator, collective coherent coupling of quantum dot band-edge states and near-field proximity interaction are vital ingredients for the realization of near-field strong coupling of mesoscopic quantum dots. The broadband nature of the interaction paves the road toward ultrafast coherent manipulation of the coupled quantum dot-plasmon system under ambient conditions.

  13. An implementation problem for boson fields and quantum Girsanov transform

    Energy Technology Data Exchange (ETDEWEB)

    Ji, Un Cig, E-mail: uncigji@chungbuk.ac.kr [Department of Mathematics, Research Institute of Mathematical Finance, Chungbuk National University, Cheongju 361-763 (Korea, Republic of); Obata, Nobuaki, E-mail: obata@math.is.tohoku.ac.jp [Graduate School of Information Sciences, Tohoku University, Sendai 980-8579 (Japan)

    2016-08-15

    We study an implementation problem for quadratic functions of annihilation and creation operators on a boson field in terms of quantum white noise calculus. The implementation problem is shown to be equivalent to a linear differential equation for white noise operators containing quantum white noise derivatives. The solution is explicitly obtained and turns out to form a class of white noise operators including generalized Fourier–Gauss and Fourier–Mehler transforms, Bogoliubov transform, and a quantum extension of the Girsanov transform.

  14. An implementation problem for boson fields and quantum Girsanov transform

    International Nuclear Information System (INIS)

    Ji, Un Cig; Obata, Nobuaki

    2016-01-01

    We study an implementation problem for quadratic functions of annihilation and creation operators on a boson field in terms of quantum white noise calculus. The implementation problem is shown to be equivalent to a linear differential equation for white noise operators containing quantum white noise derivatives. The solution is explicitly obtained and turns out to form a class of white noise operators including generalized Fourier–Gauss and Fourier–Mehler transforms, Bogoliubov transform, and a quantum extension of the Girsanov transform.

  15. Motivating quantum field theory: the boosted particle in a box

    International Nuclear Information System (INIS)

    Vutha, Amar C

    2013-01-01

    It is a maxim often stated, yet rarely illustrated, that the combination of special relativity and quantum mechanics necessarily leads to quantum field theory. An elementary illustration is provided using the familiar particle in a box, boosted to relativistic speeds. It is shown that quantum fluctuations of momentum lead to energy fluctuations, which are inexplicable without a framework that endows the vacuum with dynamical degrees of freedom and allows particle creation/annihilation. (letters and comments)

  16. Quantum scattering from classical field theory

    International Nuclear Information System (INIS)

    Gould, T.M.; Poppitz, E.R.

    1995-01-01

    We show that scattering amplitudes between initial wave packet states and certain coherent final states can be computed in a systematic weak coupling expansion about classical solutions satisfying initial-value conditions. The initial-value conditions are such as to make the solution of the classical field equations amenable to numerical methods. We propose a practical procedure for computing classical solutions which contribute to high energy two-particle scattering amplitudes. We consider in this regard the implications of a recent numerical simulation in classical SU(2) Yang-Mills theory for multiparticle scattering in quantum gauge theories and speculate on its generalization to electroweak theory. We also generalize our results to the case of complex trajectories and discuss the prospects for finding a solution to the resulting complex boundary value problem, which would allow the application of our method to any wave packet to coherent state transition. Finally, we discuss the relevance of these results to the issues of baryon number violation and multiparticle scattering at high energies. ((orig.))

  17. Quantum field theory on higher-genus Riemann surfaces, 2

    International Nuclear Information System (INIS)

    Kubo, Reijiro; Ojima, Shuichi.

    1990-08-01

    Quantum field theory for closed bosonic string systems is formulated on arbitrary higher-genus Riemann surfaces in global operator formalism. Canonical commutation relations between bosonic string field X μ and their conjugate momenta P ν are derived in the framework of conventional quantum field theory. Problems arising in quantizing bosonic systems are considered in detail. Applying the method exploited in the preceding paper we calculate Ward-Takahashi identities. (author)

  18. Wave packet revivals in a graphene quantum dot in a perpendicular magnetic field

    International Nuclear Information System (INIS)

    Torres, J. J.; Romera, E.

    2010-01-01

    We study the time evolution of localized wave packets in graphene quantum dots in a perpendicular magnetic field, focusing on the quasiclassical and revival periodicities, for different values of the magnetic field intensities in a theoretical framework. We have considered contributions of the two inequivalent points in the Brillouin zone. The revival time has been found as an observable that shows the break valley degeneracy.

  19. Slow dynamics at critical points: the field-theoretical perspective

    International Nuclear Information System (INIS)

    Gambassi, Andrea

    2006-01-01

    The dynamics at a critical point provides a simple instance of slow collective evolution, characterised by aging phenomena and by a violation of the fluctuation-dissipation relation even for long times. By virtue of the universality in critical phenomena it is possible to provide quantitative predictions for some aspects of these behaviours by field-theoretical methods. We review some of the theoretical results that have been obtained in recent years for the relevant (universal) quantities, such as the fluctuation-dissipation ratio, associated with the non-equilibrium critical dynamics

  20. Quantum field theory in curved spacetime and black hole thermodynamics

    CERN Document Server

    Wald, Robert M

    1994-01-01

    In this book, Robert Wald provides a coherent, pedagogical introduction to the formulation of quantum field theory in curved spacetime. He begins with a treatment of the ordinary one-dimensional quantum harmonic oscillator, progresses through the construction of quantum field theory in flat spacetime to possible constructions of quantum field theory in curved spacetime, and, ultimately, to an algebraic formulation of the theory. In his presentation, Wald disentangles essential features of the theory from inessential ones (such as a particle interpretation) and clarifies relationships between various approaches to the formulation of the theory. He also provides a comprehensive, up-to-date account of the Unruh effect, the Hawking effect, and some of its ramifications. In particular, the subject of black hole thermodynamics, which remains an active area of research, is treated in depth. This book will be accessible to students and researchers who have had introductory courses in general relativity and quantum f...

  1. Near-field optical spectroscopy of semiconductor quantum wires

    Science.gov (United States)

    Gershoni, D.; Harris, T. D.; Pfeiffer, L. N.

    1997-09-01

    We discuss low temperature near-field scanning optical spectroscopical studies of single, nanometer dimension, cleaved edge overgrown quantum wires. We use the enhanced spatial resolution of near-field microscopy, to spectroscopically investigate these single wires, which are inaccessible to conventional far-field optical spectroscopy. We thus performed a direct experimental comparison between a two-dimensional quantum system and a single genuine one-dimensional quantum system. We show that the photoluminescence of a single quantum wire is easily distinguished from that of the surrounding quantum well. Emission from localized centers is shown to dominate the photoluminescence from both wires and wells at low temperatures. A factor of three enhancement in the optical absorption of a wire, in comparison with that of a similar well, is concluded from the photoluminescence excitation data.

  2. Quantum field theory II introductions to quantum gravity, supersymmetry and string theory

    CERN Document Server

    Manoukian, Edouard B

    2016-01-01

    This book takes a pedagogical approach to explaining quantum gravity, supersymmetry and string theory in a coherent way. It is aimed at graduate students and researchers in quantum field theory and high-energy physics. The first part of the book introduces quantum gravity, without requiring previous knowledge of general relativity (GR). The necessary geometrical aspects are derived afresh leading to explicit general Lagrangians for gravity, including that of general relativity. The quantum aspect of gravitation, as described by the graviton, is introduced and perturbative quantum GR is discussed. The Schwinger-DeWitt formalism is developed to compute the one-loop contribution to the theory and renormalizability aspects of the perturbative theory are also discussed. This follows by introducing only the very basics of a non-perturbative, background-independent, formulation of quantum gravity, referred to as “loop quantum gravity”, which gives rise to a quantization of space. In the second part the author in...

  3. On the relation of the theoretical foundations of quantum theory and general relativity theory

    International Nuclear Information System (INIS)

    Kober, Martin

    2010-01-01

    The specific content of the present thesis is presented in the following way. First the most important contents of quantum theory and general relativity theory are presented. In connection with the general relativity theory the mathematical property of the diffeomorphism invariance plays the deciding role, while concerning the quantum theory starting from the Copenhagen interpretation first the measurement problem is treated, before basing on the analysis of concrete phenomena and the mathematical apparatus of quantum theory the nonlocality is brought into focus as an important property. This means that both theories suggest a relationalistic view of the nature of the space. This analysis of the theoretical foundations of quantum theory and general relativity theory in relation to the nature of the space obtains only under inclusion of Kant's philosophy and his analysis of the terms space and time as fundamental forms of perception its full persuasive power. Then von Weizsaeckers quantum theory of the ur-alternatives is presented. Finally attempts are made to apply the obtained knowledge to the question of the quantum-theoretical formulation of general relativity theory.

  4. Coupled field induced conversion between destructive and constructive quantum interference

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Xiangqian, E-mail: xqjiang@hit.edu.cn; Sun, Xiudong

    2016-12-15

    We study the control of quantum interference in a four-level atom driven by three coherent fields forming a closed loop. The spontaneous emission spectrum shows two sets of peaks which are dramatically influenced by the fields. Due to destructive quantum interference, a dark line can be observed in the emission spectrum, and the condition of the dark line is given. We found that the conversion between destructive and constructive quantum interference can be achieved through controlling the Rabi frequency of the external fields.

  5. High-field spin dynamics of antiferromagnetic quantum spin chains

    DEFF Research Database (Denmark)

    Enderle, M.; Regnault, L.P.; Broholm, C.

    2000-01-01

    present recent work on the high-field spin dynamics of the S = I antiferromagnetic Heisenberg chains NENP (Haldane ground state) and CsNiCl3 (quasi-1D HAF close to the quantum critical point), the uniform S = 1/2 chain CTS, and the spin-Peierls system CuGeO3. (C) 2000 Elsevier Science B,V. All rights......The characteristic internal order of macroscopic quantum ground states in one-dimensional spin systems is usually not directly accessible, but reflected in the spin dynamics and the field dependence of the magnetic excitations. In high magnetic fields quantum phase transitions are expected. We...

  6. Ultrafast Gain Dynamics in Quantum Dot Amplifiers: Theoretical Analysis and Experimental Investigations

    DEFF Research Database (Denmark)

    Poel, Mike van der; Gehrig, Edeltraud; Hess, Ortwin

    2005-01-01

    Ultrafast gain dynamics in an optical amplifier with an active layer of self-organized quantum dots (QDs) emitting near 1.3$muhbox m$is characterized experimentally in a pump-probe experiment and modeled theoretically on the basis of QD Maxwell–Bloch equations. Experiment and theory are in good a...

  7. Physics in one dimension: theoretical concepts for quantum many-body systems.

    Science.gov (United States)

    Schönhammer, K

    2013-01-09

    Various sophisticated approximation methods exist for the description of quantum many-body systems. It was realized early on that the theoretical description can simplify considerably in one-dimensional systems and various exact solutions exist. The focus in this introductory paper is on fermionic systems and the emergence of the Luttinger liquid concept.

  8. Representations of homogeneous quantum Lévy fields

    Indian Academy of Sciences (India)

    Dedicated to K B Sinha on the event of his 60th birthday. Abstract. We study homogeneous quantum Lévy processes and fields with independent additive increments ... The problem of reconstructing a quantum Lévy process in the narrow sense is then reduced to finding a representation of the cumulant generating state and ...

  9. From PT -symmetric quantum mechanics to conformal field theory

    Indian Academy of Sciences (India)

    ing Yang–Lee model, a quantum field theory with cubic interaction and purely imaginary coupling. We give a ... factor approach for correlation functions [6,7], the exact off-critical g-function [8,9], the excited state and the ...... related to their full consistency as quantum mechanical models have been success- fully addressed.

  10. From PT-symmetric quantum mechanics to conformal field theory

    Indian Academy of Sciences (India)

    One of the simplest examples of a P T -symmetric quantum system is the scaling Yang–Lee model, a quantum field theory with cubic interaction and purely imaginary coupling. We give a historical review of some facts about this model in ≤ 2 dimensions, from its original definition in connection with phase transitions in the ...

  11. Quantum epistemology from subquantum ontology: Quantum mechanics from theory of classical random fields

    Science.gov (United States)

    Khrennikov, Andrei

    2017-02-01

    The scientific methodology based on two descriptive levels, ontic (reality as it is) and epistemic (observational), is briefly presented. Following Schrödinger, we point to the possible gap between these two descriptions. Our main aim is to show that, although ontic entities may be unaccessible for observations, they can be useful for clarification of the physical nature of operational epistemic entities. We illustrate this thesis by the concrete example: starting with the concrete ontic model preceding quantum mechanics (the latter is treated as an epistemic model), namely, prequantum classical statistical field theory (PCSFT), we propose the natural physical interpretation for the basic quantum mechanical entity-the quantum state ("wave function"). The correspondence PCSFT ↦ QM is not straightforward, it couples the covariance operators of classical (prequantum) random fields with the quantum density operators. We use this correspondence to clarify the physical meaning of the pure quantum state and the superposition principle-by using the formalism of classical field correlations. In classical mechanics the phase space description can be considered as the ontic description, here states are given by points λ =(x , p) of phase space. The dynamics of the ontic state is given by the system of Hamiltonian equations.We can also consider probability distributions on the phase space (or equivalently random variables valued in it). We call them probabilistic ontic states. Dynamics of probabilistic ontic states is given by the Liouville equation.In classical physics we can (at least in principle) measure both the coordinate and momentum and hence ontic states can be treated as epistemic states as well (or it is better to say that here epistemic states can be treated as ontic states). Probabilistic ontic states represent probabilities for outcomes of joint measurement of position and momentum.However, this was a very special, although very important, example of

  12. Quantum Wells, Wires and Dots Theoretical and Computational Physics of Semiconductor Nanostructures

    CERN Document Server

    Harrison, Paul

    2011-01-01

    Quantum Wells, Wires and Dots, 3rd Edition is aimed at providing all the essential information, both theoretical and computational, in order that the reader can, starting from essentially nothing, understand how the electronic, optical and transport properties of semiconductor heterostructures are calculated. Completely revised and updated, this text is designed to lead the reader through a series of simple theoretical and computational implementations, and slowly build from solid foundations, to a level where the reader can begin to initiate theoretical investigations or explanations of their

  13. Synthesis of Quantum Antennas for Shaping Field Correlations

    Science.gov (United States)

    Mikhalychev, A.; Mogilevtsev, D.; Slepyan, G. Ya.; Karuseichyk, I.; Buchs, G.; Boiko, D. L.; Boag, A.

    2018-02-01

    We present a method to design an initial state in a quantum antenna in order to shape the emitted field higher-order correlation functions at will. This method is based on quantum state reconstruction techniques and relies on an entanglement of the emitters. We show that even the simplest antenna arrangements such as linear dipole arrays can exhibit a large variability in the emitted field-correlation function patterns, including, e.g., the generation of highly codirectional and contradirectional correlated twin photons, as well as multiphoton entangled states. Moreover, we identify a class of initial states that lead to a complete suppression of the field in the far-field zone. We also demonstrate the possibility to use a modified semiclassical approach for designing quantum antennas, simplifying the antenna state inference task. Our approach can find applications in the development of future quantum optics devices and methods, such as quantum sources for superresolution quantum imaging, high-precision sensing, as well as emitter-field interfaces for quantum information processing systems.

  14. Advancements in the Field of Quantum Dots

    Science.gov (United States)

    Mishra, Sambeet; Tripathy, Pratyasha; Sinha, Swami Prasad.

    2012-08-01

    Quantum dots are defined as very small semiconductor crystals of size varying from nanometer scale to a few micron i.e. so small that they are considered dimensionless and are capable of showing many chemical properties by virtue of which they tend to be lead at one minute and gold at the second minute.Quantum dots house the electrons just the way the electrons would have been present in an atom, by applying a voltage. And therefore they are very judiciously given the name of being called as the artificial atoms. This application of voltage may also lead to the modification of the chemical nature of the material anytime it is desired, resulting in lead at one minute to gold at the other minute. But this method is quite beyond our reach. A quantum dot is basically a semiconductor of very tiny size and this special phenomenon of quantum dot, causes the band of energies to change into discrete energy levels. Band gaps and the related energy depend on the relationship between the size of the crystal and the exciton radius. The height and energy between different energy levels varies inversely with the size of the quantum dot. The smaller the quantum dot, the higher is the energy possessed by it.There are many applications of the quantum dots e.g. they are very wisely applied to:Light emitting diodes: LEDs eg. White LEDs, Photovoltaic devices: solar cells, Memory elements, Biology : =biosensors, imaging, Lasers, Quantum computation, Flat-panel displays, Photodetectors, Life sciences and so on and so forth.The nanometer sized particles are able to display any chosen colour in the entire ultraviolet visible spectrum through a small change in their size or composition.

  15. Mathematica® for Theoretical Physics Electrodynamics, Quantum Mechanics, General Relativity and Fractals

    CERN Document Server

    Baumann, Gerd

    2005-01-01

    Mathematica for Theoretical Physics: Electrodynamics, Quantum Mechanics, General Relativity, and Fractals This second edition of Baumann's Mathematica® in Theoretical Physics shows readers how to solve physical problems and deal with their underlying theoretical concepts while using Mathematica® to derive numeric and symbolic solutions. Each example and calculation can be evaluated by the reader, and the reader can change the example calculations and adopt the given code to related or similar problems. The second edition has been completely revised and expanded into two volumes: The first volume covers classical mechanics and nonlinear dynamics. Both topics are the basis of a regular mechanics course. The second volume covers electrodynamics, quantum mechanics, relativity, and fractals and fractional calculus. New examples have been added and the representation has been reworked to provide a more interactive problem-solving presentation. This book can be used as a textbook or as a reference work, by student...

  16. A novel connection between scalar field theories and quantum mechanics

    Science.gov (United States)

    Bazeia, D.; Losano, L.

    2018-01-01

    This work deals with scalar field theories and supersymmetric quantum mechanics. The investigation is inspired by a recent result, which shows how to use the reconstruction mechanism to describe two distinct field theories from the very same quantum mechanics potential, and by an older work, which describes the deformation procedure that offers an interesting way to generate and solve new scalar field theories, starting from a given model of current interest. We use the procedure to unveil a new route, from which one can describe families of scalar field theories that engender the very same quantum mechanics potential. The approach can be applied algorithmically, and implemented to generate models that give rise to distinct quantum mechanics systems as well.

  17. The consistent histories interpretation of quantum fields in curved spacetime

    International Nuclear Information System (INIS)

    Blencowe, M.

    1991-01-01

    As an initial attempt to address some of the foundation problems of quantum mechanics, the author formulates the consistent histories interpretation of quantum field theory on a globally hyperbolic curved space time. He then constructs quasiclassical histories for a free, massive scalar field. In the final part, he points out the shortcomings of the theory and conjecture that one must take into account the fact that gravity is quantized in order to overcome them

  18. Measuring the quantum state of the electromagnetic field

    International Nuclear Information System (INIS)

    Davidovich, L.

    1999-01-01

    Recent experiments in cavity QED have allowed the monitoring of the decoherence process, which is at heart of the quantum theory of measurement and plays an essential role in the classical limit of quantum mechanics. An important ingredient of these experiments is the ability to probe the quantum state of the electromagnetic field in a cavity, and to distinguish a coherent superposition of two distinct coherent states of the field from a statistical mixture of the same states. After reviewing some of the methods recently developed to measure the quantum state of the electromagnetic field, it is shown here that the technique of Ramsey interferometry central to those experiments, may be used to determine completely the quantum state of an electromagnetic field in a cavity. This new method, which allows the direct measurement of the Wigner function of the field, is a useful tool for probing the quantum-classical transition and, in particular, the decoherence of superpositions of distinguishable coherent states of the electromagnetic field in the cavity. (author)

  19. Theoretical studies on nuclear spin selective quantum dynamics of non-linear molecules

    International Nuclear Information System (INIS)

    Grohmann, Thomas

    2012-01-01

    In this thesis the wave packet dynamics of nuclear spin isomers of polyatomic molecules after interaction with static and time-dependent magnetic fields and moderate intense nonresonant laser pulses is investigated. In particular, the process of inducing (internal) molecular rotation as well as alignment of molecules by manipulating their rotational or rotational-torsional degrees of freedom is studied. In the first part of the thesis all theoretical concepts for identifying nuclear spin isomers and for describing their quantum dynamics will be discussed. Especially the symmetrization postulate and themolecular symmetry group will be introduced and illustrated for some examples of molecules. These concepts will be extended to the case of identifying nuclear spin isomers in the presence of an external field. In the second part it is shown for nitromethane that magnetic fields are able to induce unidirectional rotations in opposite directions for different nuclear spin isomers of molecules containing methyl groups if the dipolar interaction is included. Additionally, it is demonstrated that different nuclear spin isomers of a chemical compound may show different alignment after the interaction with a moderate intense laser pulse. As shown for the rigid symmetric top propadien and the rigid asymmetric tops ethene and analogues, distinct pairs of nuclear spin isomers show at certain points in time a complementary behavior: while one isomer is showing alignment the partner isomer is showing anti-alignment. Moreover, it is illustrated that not every nuclear spin isomer can be aligned equally efficient. The alignment of non-rigid molecules is considered as well. As an example for a molecule with feasible torsion in the electronic ground state, the alignment of diboron tetrafluoride is investigated. It becomes apparent that not only rotational but also the torsional dynamics of the molecules is nuclear spin selective; different nuclear spin isomers have at distinct points

  20. Quantum perceptron over a field and neural network architecture selection in a quantum computer.

    Science.gov (United States)

    da Silva, Adenilton José; Ludermir, Teresa Bernarda; de Oliveira, Wilson Rosa

    2016-04-01

    In this work, we propose a quantum neural network named quantum perceptron over a field (QPF). Quantum computers are not yet a reality and the models and algorithms proposed in this work cannot be simulated in actual (or classical) computers. QPF is a direct generalization of a classical perceptron and solves some drawbacks found in previous models of quantum perceptrons. We also present a learning algorithm named Superposition based Architecture Learning algorithm (SAL) that optimizes the neural network weights and architectures. SAL searches for the best architecture in a finite set of neural network architectures with linear time over the number of patterns in the training set. SAL is the first learning algorithm to determine neural network architectures in polynomial time. This speedup is obtained by the use of quantum parallelism and a non-linear quantum operator. Copyright © 2016 Elsevier Ltd. All rights reserved.

  1. Theoretical investigations of quantum correlations in NMR multiple-pulse spin-locking experiments

    Science.gov (United States)

    Gerasev, S. A.; Fedorova, A. V.; Fel'dman, E. B.; Kuznetsova, E. I.

    2018-04-01

    Quantum correlations are investigated theoretically in a two-spin system with the dipole-dipole interactions in the NMR multiple-pulse spin-locking experiments. We consider two schemes of the multiple-pulse spin-locking. The first scheme consists of π /2-pulses only and the delays between the pulses can differ. The second scheme contains φ-pulses (0Quantum discord is obtained for the first scheme of the multiple-pulse spin-locking experiment at different temperatures.

  2. Finite field-dependent symmetries in perturbative quantum gravity

    International Nuclear Information System (INIS)

    Upadhyay, Sudhaker

    2014-01-01

    In this paper we discuss the absolutely anticommuting nilpotent symmetries for perturbative quantum gravity in general curved spacetime in linear and non-linear gauges. Further, we analyze the finite field-dependent BRST (FFBRST) transformation for perturbative quantum gravity in general curved spacetime. The FFBRST transformation changes the gauge-fixing and ghost parts of the perturbative quantum gravity within functional integration. However, the operation of such symmetry transformation on the generating functional of perturbative quantum gravity does not affect the theory on physical ground. The FFBRST transformation with appropriate choices of finite BRST parameter connects non-linear Curci–Ferrari and Landau gauges of perturbative quantum gravity. The validity of the results is also established at quantum level using Batalin–Vilkovisky (BV) formulation. -- Highlights: •The perturbative quantum gravity is treated as gauge theory. •BRST and anti-BRST transformations are developed in linear and non-linear gauges. •BRST transformation is generalized by making it finite and field dependent. •Connection between linear and non-linear gauges is established. •Using BV formulation the results are established at quantum level also

  3. Statistical methods in quantum optics 2 non-classical fields

    CERN Document Server

    Carmichael, H J

    2007-01-01

    Statistical Methods in Quantum Optics 2 - Non-Classical Fields continues the development of the methods used in quantum optics to treat open quantum systems and their fluctuations. Its early chapters build upon the phase-space methods introduced in the first volume Statistical Methods in Quantum Optics 1 - Matter Equations and Fokker-Planck Equations: the difficulties these methods face in treating non-classical light are exposed, where the regime of large fluctuations – failure of the system size expansion – is shown to be particularly problematic. Cavity QED is adopted as a natural vehicle for extending quantum noise theory into this regime. In response to the issues raised, the theory of quantum trajectories is presented as a universal approach to the treatment of fluctuations in open quantum systems. This book presents its material at a level suitable for beginning researchers or students in an advanced course in quantum optics, or a course in quantum mechanics or statistical physics that deals with o...

  4. Measurement of gravity and gauge fields using quantum mechanical probes

    International Nuclear Information System (INIS)

    Anandan, J.

    1986-01-01

    The author considers the question of which quantities are observed when the gravitational and gauge fields are measured by a quantum mechanical probe. The motion of a quantum mechanical particle can be constructed, via Huyghens' principle, by the interference of secondary wavelets. Three types of interference phenomena are considered: interference of two coherent beams separated in space-time during part of their motion; interference of two coherent beams which are in the same region in spacetime but differ in energy or mass; and the Josphson effect and its generalization. The author shows how to determine the gravitational field by means of quantum interference. The corresponding problem for gauge fields is treated and a simple proof of the previously proved theorem for the reconstruction of the connection from the holonomy transformations is presented. A heuristic principle for the gravitational interaction of two quantum mechanical particles is formulated which implies the equivalence of inertial and active gravitational masses

  5. On the scaling limits in the Euclidean (quantum) field theory

    International Nuclear Information System (INIS)

    Gielerak, R.

    1983-01-01

    The author studies the concept of scaling limits in the context of the constructive field theory. He finds that the domain of attraction of a free massless Euclidean scalar field in the two-dimensional space time contains almost all Euclidean self-interacting models of quantum fields so far constructed. The renormalized scaling limit of the Wick polynomials of several self-interacting Euclidean field theory models are shown to be the same as in the free field theory. (Auth.)

  6. Electric field control of emergent electrodynamics in quantum spin ice

    Science.gov (United States)

    Lantagne-Hurtubise, Étienne; Bhattacharjee, Subhro; Moessner, R.

    2017-09-01

    We study the coupling between conventional (Maxwell) and emergent electrodynamics in quantum spin ice, a 3+1-dimensional U (1 ) quantum spin liquid. We find that a uniform electric field can be used to tune the properties of both the ground state and excitations of the spin liquid. In particular, it induces emergent birefringence, rendering the speed of the emergent light anisotropic and polarization-dependent. A sufficiently strong electric field triggers a quantum phase transition into new U (1 ) quantum spin liquid phases, which trap emergent electric π fluxes. The flux patterns of these new phases depend on the direction of the electric field. Strikingly, some of the canonical pinch points in the spin structure factor, characteristic of classical spin ice, emerge near the phase transition, while they are absent in the quantum spin liquid phases. Estimating the electric field strength required, we find that this transition is potentially accessible experimentally. Finally, we propose a minimal mechanism by which an oscillating electric field can generate emergent radiation inside a quantum spin ice material with non-Kramers spin doublets.

  7. Differentiability and continuity of quantum fields on a lattice

    International Nuclear Information System (INIS)

    deLyra, J.L.; Foong, S.K.; Gallivan, T.E.

    1991-01-01

    The differentiability and continuity properties of quantized bosonic fields on a lattice are examined. It is shown for free fields that, in the continuum limit, the dominant configurations in the functional integral become discontinuous when the spacetime dimension is greater than 1. It is argued that the same is true for interacting fields. This is unlike the one-dimensional case of quantum mechanics, in which the dominant configurations are continuous but not differentiable. As a consequence of this discontinuity, classically equivalent actions may produce inequivalent quantum field theories upon functional-integral quantization

  8. BOOK REVIEW: Quantum Field Theory in a Nutshell (2nd edn) Quantum Field Theory in a Nutshell (2nd edn)

    Science.gov (United States)

    Peskin, Michael E.

    2011-04-01

    Anthony Zee is not only a leading theoretical physicist but also an author of popular books on both physics and non-physics topics. I recommend especially `Swallowing Clouds', on Chinese cooking and its folklore. Thus, it is not surprising that his textbook has a unique flavor. Derivations end, not with `QED' but with exclamation points. At the end of one argument, we read `Vive Cauchy!', in another `the theorem practically exudes generality'. This is quantum field theory taught at the knee of an eccentric uncle; one who loves the grandeur of his subject, has a keen eye for a slick argument, and is eager to share his repertoire of anecdotes about Feynman, Fermi, and all of his heroes. A one-page section entitled `Electric Charge' illustrates the depth and tone of the book. In the previous section, Zee has computed the Feynman diagram responsible for vacuum polarization, in which a photon converts briefly to a virtual electron-positron pair. In the first paragraph, he evaluates this expression, giving a concrete formula for the momentum-dependence of the electric charge, an important effect of quantum field theory. Next, he dismisses other possible diagrams that could affect the value of the electric charge. Most authors would give an explicit argument that these diagrams cancel, but for Zee it is more important to make the point that this result is expected and, from the right point of view, obvious. Finally, he discusses the implications for the relative size of the charges of the electron and the proton. If the magnitudes of charges are affected by interactions, and the proton has strong interactions but the electron does not, can it make sense that the charges of the proton and the electron are exactly equal and opposite? The answer is yes, and also that this was the real point of the whole derivation. The book takes on the full range of topics covered in typical graduate course in quantum field theory, and many additional topics: magnetic monopoles, solitons

  9. Silicon Carbide Defect Qubits/Quantum Memory with Field-Tuning: OSD Quantum Science and Engineering Program (QSEP)

    Science.gov (United States)

    2017-08-01

    TECHNICAL REPORT 3073 August 2017 Silicon Carbide Defect Qubits/Quantum Memory with Field-tuning: OSD Quantum Science and Engineering Program...Pacific personnel and working towards supporting demonstrations of quantum entanglement based on these qubits and quantum memories developed out of the...EFFECT OF FIELD-EFFECT TUNINING ....11 5. QUBIT/QUANTUM MEMORY DEVICE DESIGN AND FABRICATION ..............................12 5.1 DEVICE DESIGN

  10. What have we learned from quantum field theory in curved space-time

    International Nuclear Information System (INIS)

    Fulling, S.A.

    1984-01-01

    The paper reviews the quantum field theory in curved space-time. Field quantization in gravitational backgrounds; particle creation by black holes; Hawking radiation; quantum field theory in curved space-time; covariant renormalization of the stress-energy-momentum tensor; quantum field theory and quantum gravity; are all discussed. (U.K.)

  11. Theoretical study of phosphorene tunneling field effect transistors

    Energy Technology Data Exchange (ETDEWEB)

    Chang, Jiwon; Hobbs, Chris [SEMATECH, 257 Fuller Rd #2200, Albany, New York 12203 (United States)

    2015-02-23

    In this work, device performances of tunneling field effect transistors (TFETs) based on phosphorene are explored via self-consistent atomistic quantum transport simulations. Phosphorene is an ultra-thin two-dimensional (2-D) material with a direct band gap suitable for TFETs applications. Our simulation shows that phosphorene TFETs exhibit subthreshold slope below 60 mV/dec and a wide range of on-current depending on the transport direction due to highly anisotropic band structures of phosphorene. By benchmarking with monolayer MoTe{sub 2} TFETs, we predict that phosphorene TFETs oriented in the small effective mass direction can yield much larger on-current at the same on-current/off-current ratio than monolayer MoTe{sub 2} TFETs. It is also observed that a gate underlap structure is required for scaling down phosphorene TFETs in the small effective mass direction to suppress the source-to-drain direct tunneling leakage current.

  12. Hydrogen atom as test field of theoretical models

    International Nuclear Information System (INIS)

    Baiquni, A.

    1976-01-01

    Semi classical theory, covering Bohr atom theory, Bohr Sommerfeld theory, Sommerfeld relativistic theory, and quantum theory such as particle and complementarity dualism, wave mechanics, approximation method, relativistic quantum mechanics, and hydrogen atom fine structure, are discussed. (SMN)

  13. Dirac fields in loop quantum gravity and big bang nucleosynthesis

    International Nuclear Information System (INIS)

    Bojowald, Martin; Das, Rupam; Scherrer, Robert J.

    2008-01-01

    Big bang nucleosynthesis requires a fine balance between equations of state for photons and relativistic fermions. Several corrections to equation of state parameters arise from classical and quantum physics, which are derived here from a canonical perspective. In particular, loop quantum gravity allows one to compute quantum gravity corrections for Maxwell and Dirac fields. Although the classical actions are very different, quantum corrections to the equation of state are remarkably similar. To lowest order, these corrections take the form of an overall expansion-dependent multiplicative factor in the total density. We use these results, along with the predictions of big bang nucleosynthesis, to place bounds on these corrections and especially the patch size of discrete quantum gravity states.

  14. Cosmology from group field theory formalism for quantum gravity.

    Science.gov (United States)

    Gielen, Steffen; Oriti, Daniele; Sindoni, Lorenzo

    2013-07-19

    We identify a class of condensate states in the group field theory (GFT) formulation of quantum gravity that can be interpreted as macroscopic homogeneous spatial geometries. We then extract the dynamics of such condensate states directly from the fundamental quantum GFT dynamics, following the procedure used in ordinary quantum fluids. The effective dynamics is a nonlinear and nonlocal extension of quantum cosmology. We also show that any GFT model with a kinetic term of Laplacian type gives rise, in a semiclassical (WKB) approximation and in the isotropic case, to a modified Friedmann equation. This is the first concrete, general procedure for extracting an effective cosmological dynamics directly from a fundamental theory of quantum geometry.

  15. Quantum scar and breakdown of universality in graphene: A theoretical insight

    Science.gov (United States)

    Iyakutti, Kombiah; Rajeswarapalanichamy, Ratnavelu; Surya, Velappa Jayaraman; Kawazoe, Yoshiyuki

    2017-12-01

    Graphene has brought forward a lot of new physics. One of them is the emergence of massless Dirac fermions in addition to the electrons and these features are new to physics. In this theoretical study, the signatures for quantum scar and the breakdown of universality in graphene are investigated with reference to the presence of these two types of fermions. Taking the graphene quantum dot (QD) potential as the confining potential, the radial part of Dirac equations are solved numerically. Concentrations of the two component eigen-wavefunctions about classical periodic orbits emerge as the signatures for the quantum scar. The sudden variations, in the ratio of the radial wave-functions (large and small components), R(g/f), with mass ratio κ are the signatures for breakdown of universality in graphene. The breakdown of universality occurs for the states k = ‑1 and k = 1, and the state k = ‑1 is more susceptible to the breakdown of universality.

  16. Evolution of Quantum Fluctuations Near the Quantum Critical Point of the Transverse Field Ising Chain System CoNb_{2}O_{6}

    Directory of Open Access Journals (Sweden)

    A. W. Kinross

    2014-07-01

    Full Text Available The transverse field Ising chain model is ideally suited for testing the fundamental ideas of quantum phase transitions because its well-known T=0 ground state can be extrapolated to finite temperatures. Nonetheless, the lack of appropriate model materials hindered the past effort to test the theoretical predictions. Here, we map the evolution of quantum fluctuations in the transverse field Ising chain based on nuclear magnetic resonance measurements of CoNb_{2}O_{6}, and we demonstrate the finite-temperature effects on quantum criticality for the first time. From the temperature dependence of the ^{93}Nb longitudinal relaxation rate 1/T_{1}, we identify the renormalized classical, quantum critical, and quantum disordered scaling regimes in the temperature (T vs transverse magnetic field (h_{⊥} phase diagram. Precisely at the critical field h_{⊥}^{c}=5.25±0.15  T, we observe a power-law behavior, 1/T_{1}∼T^{−3/4}, as predicted by quantum critical scaling. Our parameter-free comparison between the data and theory reveals that quantum fluctuations persist up to as high as T∼0.4J, where the intrachain exchange interaction J is the only energy scale of the problem.

  17. Bucharest PhD Training School : Modern Aspects of Quantum Field Theory and Applications

    CERN Document Server

    2015-01-01

    Bucharest 2015 – Modern Aspects of Quantum Field Theory is part of the CERN – SEENET-MTP PhD Training Program, which consists of a number of seminars in theoretical high energy Physics. This is the second seminar organized by this Program. Here are some photos from this event held in Bucharest between 8-14 November 2015. The previous seminar was organized in Belgrade, under the name Belgrade 2015 - Supergravity.

  18. Field theoretical prediction of a property of the tropical cyclone

    Science.gov (United States)

    Spineanu, F.; Vlad, M.

    2014-01-01

    The large scale atmospheric vortices (tropical cyclones, tornadoes) are complex physical systems combining thermodynamics and fluid-mechanical processes. The late phase of the evolution towards stationarity consists of the vorticity concentration, a well known tendency to self-organization , an universal property of the two-dimensional fluids. It may then be expected that the stationary state of the tropical cyclone has the same nature as the vortices of many other systems in nature: ideal (Euler) fluids, superconductors, Bose-Einsetin condensate, cosmic strings, etc. Indeed it was found that there is a description of the atmospheric vortex in terms of a classical field theory. It is compatible with the more conventional treatment based on conservation laws, but the field theoretical model reveals properties that are almost inaccessible to the conventional formulation: it identifies the stationary states as being close to self-duality. This is of highest importance: the self-duality is known to be the origin of all coherent structures known in natural systems. Therefore the field theoretical (FT) formulation finds that the cuasi-coherent form of the atmospheric vortex (tropical cyclone) at stationarity is an expression of this particular property. In the present work we examine a strong property of the tropical cyclone, which arises in the FT formulation in a natural way: the equality of the masses of the particles associated to the matter field and respectively to the gauge field in the FT model is translated into the equality between the maximum radial extension of the tropical cyclone and the Rossby radius. For the cases where the FT model is a good approximation we calculate characteristic quantities of the tropical cyclone and find good comparison with observational data.

  19. A Note on the Field-Theoretical Description of Superfluids

    CERN Document Server

    Andrianopoli, L; Grassi, P A; Trigiante, M

    2014-01-01

    Recently, a Lagrangian description of superfluids attracted some interest from the fluid/gravity-correspondence viewpoint. In this respect, the work of Dubovksy et al. has proposed a new field theoretical description of fluids, which has several interesting aspects. On another side, we have provided in arXiv:1304.2206 a supersymmetric extension of the original works. In the analysis of the Lagrangian structures a new invariant appeared which, although related to known invariants, provides, in our opinion, a better parametrisation of the fluid dynamics in order to describe the fluid/superfluid phases.

  20. Aspects of Nonlocality in Quantum Field Theory, Quantum Gravity and Cosmology

    CERN Document Server

    Barvinsky, A O

    2015-01-01

    This paper contains a collection of essays on nonlocal phenomena in quantum field theory, gravity and cosmology. Mechanisms of nonlocal contributions to the quantum effective action are discussed within the covariant perturbation expansion in field strengths and spacetime curvatures and the nonperturbative method based on the late time asymptotics of the heat kernel. Euclidean version of the Schwinger-Keldysh technique for quantum expectation values is presented as a special rule of obtaining the nonlocal effective equations of motion for the mean quantum field from the Euclidean effective action. This rule is applied to a new model of ghost free nonlocal cosmology which can generate the de Sitter stage of cosmological evolution at an arbitrary value of $\\varLambda$ -- a model of dark energy with its scale played by the dynamical variable that can be fixed by a kind of a scaling symmetry breaking mechanism. This model is shown to interpolate between the superhorizon phase of gravity theory mediated by a scala...

  1. Extended objects in quantum field theory - a review

    International Nuclear Information System (INIS)

    Papastamatiou, N.J.

    1986-01-01

    Extended objects seem to be required in quantum systems in a variety of situations. Monopoles, bags, and skyrmions are believed to be features of QCD or grand-unified theories. A variety of methods have been devised to describe a quantum field theory in the presence of such extended objects. In this review, the author concentrates on a model, developed over a period of years by H. Umezawa, H. Matsumoto and others. Its salient features are the creation of the extended object by means of boson transformations, the quantization through the introduction of quantum coordinates, and the extensive use of symmetry considerations to establish the exact dependence of the Heisenberg field on the quantum coordinates as well as the form of the Hamiltonian. The extension to include fermions and time-dependent objects are also treated. (Auth.)

  2. Quantum-field theories as representations of a single $^\\ast$-algebra

    OpenAIRE

    Raab, Andreas

    2013-01-01

    We show that many well-known quantum field theories emerge as representations of a single $^\\ast$-algebra. These include free quantum field theories in flat and curved space-times, lattice quantum field theories, Wightman quantum field theories, and string theories. We prove that such theories can be approximated on lattices, and we give a rigorous definition of the continuum limit of lattice quantum field theories.

  3. Dynamics of classical and quantum fields an introduction

    CERN Document Server

    Setlur, Girish S

    2014-01-01

    Dynamics of Classical and Quantum Fields: An Introduction focuses on dynamical fields in non-relativistic physics. Written by a physicist for physicists, the book is designed to help readers develop analytical skills related to classical and quantum fields at the non-relativistic level, and think about the concepts and theory through numerous problems. In-depth yet accessible, the book presents new and conventional topics in a self-contained manner that beginners would find useful. A partial list of topics covered includes: Geometrical meaning of Legendre transformation in classical mechanics Dynamical symmetries in the context of Noether's theorem The derivation of the stress energy tensor of the electromagnetic field, the expression for strain energy in elastic bodies, and the Navier Stokes equation Concepts of right and left movers in case of a Fermi gas explained Functional integration is interpreted as a limit of a sequence of ordinary integrations Path integrals for one and two quantum particles and for...

  4. Quantum well electronic states in a tilted magnetic field.

    Science.gov (United States)

    Trallero-Giner, C; Padilha, J X; Lopez-Richard, V; Marques, G E; Castelano, L K

    2017-08-16

    We report the energy spectrum and the eigenstates of conduction and uncoupled valence bands of a quantum well under the influence of a tilted magnetic field. In the framework of the envelope approximation, we implement two analytical approaches to obtain the nontrivial solutions of the tilted magnetic field: (a) the Bubnov-Galerkin spectral method and b) the perturbation theory. We discuss the validity of each method for a broad range of magnetic field intensity and orientation as well as quantum well thickness. By estimating the accuracy of the perturbation method, we provide explicit analytical solutions for quantum wells in a tilted magnetic field configuration that can be employed to study several quantitative phenomena.

  5. Perturbative algebraic quantum field theory at finite temperature

    Energy Technology Data Exchange (ETDEWEB)

    Lindner, Falk

    2013-08-15

    We present the algebraic approach to perturbative quantum field theory for the real scalar field in Minkowski spacetime. In this work we put a special emphasis on the inherent state-independence of the framework and provide a detailed analysis of the state space. The dynamics of the interacting system is constructed in a novel way by virtue of the time-slice axiom in causal perturbation theory. This method sheds new light in the connection between quantum statistical dynamics and perturbative quantum field theory. In particular it allows the explicit construction of the KMS and vacuum state for the interacting, massive Klein-Gordon field which implies the absence of infrared divergences of the interacting theory at finite temperature, in particular for the interacting Wightman and time-ordered functions.

  6. Concepts in quantum field theory a practitioner's toolkit

    CERN Document Server

    Ilisie, Victor

    2015-01-01

    This book uses less strict yet still formal mathematical language to clarify a variety of concepts in Quantum Field Theory that remain somewhat “fuzzy” in many books designed for undergraduates and fresh graduates. The aim is not to replace formal books on Quantum Field Theory, but rather to offer a helpful complementary tool for beginners in the field. Features include a reader-friendly introduction to tensor calculus and the concept of manifolds; a simple and robust treatment for dimensional regularization; a consistent explanation of the renormalization procedure, step by step and in a transparent manner at all orders, using the QED Lagrangian; and extensive treatment of infrared as well as ultraviolet divergences. The most general (Lorentz invariant) form of Noether's theorem is presented and applied to a few simple yet relevant examples in Quantum Field Theory. These and further interesting topics are addressed in a way that will be accessible for the target readership. Some familiarity with basic no...

  7. Random walks, critical phenomena, and triviality in quantum field theory

    International Nuclear Information System (INIS)

    Fernandez, R.; Froehlich, J.; Sokal, A.D.

    1992-01-01

    The subject of this book is equilibrium statistical mechanics - in particular the theory of critical phenomena - and quantum field theory. A general review of the theory of critical phenomena in spin systems, field theories, and random-walk and random-surface models is presented. Among the more technical topics treated in this book, the central theme is the use of random-walk representations as a tool to derive correlation inequalities. The consequences of these inequalities for critical-exponent theory and the triviality question in quantum field theory are expounded in detail. The book contains some previously unpublished results. It addresses both the researcher and the graduate student in modern statistical mechanics and quantum field theory. (orig.)

  8. Nonlinear boundary value problems in quantum field theory

    International Nuclear Information System (INIS)

    Schrader, R.

    1989-01-01

    We discuss the general structure of a quantum field theory which is free in the interior of a bounded set B of R n . It is shown how to recover the field theory in the interior of B from a certain quantum field theory on the boundary. With an application to string theory in mind, we discuss the example where B equals an interval and the boundary value problem is given in terms of a euclidean functional integral with a P(var phi) interaction restricted to the boundary. copyright 1989 Academic Press, Inc

  9. Quantum fields in a big-crunch-big-bang spacetime

    International Nuclear Information System (INIS)

    Tolley, Andrew J.; Turok, Neil

    2002-01-01

    We consider quantum field theory on a spacetime representing the big-crunch-big-bang transition postulated in ekpyrotic or cyclic cosmologies. We show via several independent methods that an essentially unique matching rule holds connecting the incoming state, in which a single extra dimension shrinks to zero, to the outgoing state in which it reexpands at the same rate. For free fields in our construction there is no particle production from the incoming adiabatic vacuum. When interactions are included the particle production for fixed external momentum is finite at the tree level. We discuss a formal correspondence between our construction and quantum field theory on de Sitter spacetime

  10. Chameleon fields, wave function collapse and quantum gravity

    International Nuclear Information System (INIS)

    Zanzi, A

    2015-01-01

    Chameleon fields are quantum (usually scalar) fields, with a density-dependent mass. In a high-density environment, the mass of the chameleon is large. On the contrary, in a small-density environment (e.g. on cosmological distances), the chameleon is very light. A model where the collapse of the wave function is induced by chameleon fields is presented. During this analysis, a Chameleonic Equivalence Principle (CEP) will be formulated: in this model, quantum gravitation is equivalent to a conformal anomaly. Further research efforts are necessary to verify whether this proposal is compatible with phenomeno logical constraints. (paper)

  11. Maier-Saupe nematogenic fluid: field theoretical approach

    Directory of Open Access Journals (Sweden)

    M. Holovko

    2011-09-01

    Full Text Available We adopt a field theoretical approach to study the structure and thermodynamics of a homogeneous Maier-Saupe nematogenic fluid interacting with anisotropic Yukawa potential. In the mean field approximation we retrieve the standard Maier-Saupe theory for liquid crystals. In this theory the density is expressed via the second order Legendre polynomial of molecule orientations. In the Gaussian approximation we obtain analytical expressions for the correlation functions, the elasticity constant, the free energy, the pressure, and the chemical potential. We also use Ward symmetry identities to set a simple condition for the correlation functions. Subsequently we find corrections due to fluctuations and show that density now contains Legendre polynomials of higher orders.

  12. Electromagnetic fields with vanishing quantum corrections

    Czech Academy of Sciences Publication Activity Database

    Ortaggio, Marcello; Pravda, Vojtěch

    2018-01-01

    Roč. 779, 10 April (2018), s. 393-395 ISSN 0370-2693 R&D Projects: GA ČR GA13-10042S Institutional support: RVO:67985840 Keywords : nonlinear electrodynamics * quantum corrections Subject RIV: BA - General Mathematics OBOR OECD: Applied mathematics Impact factor: 4.807, year: 2016 https://www.sciencedirect.com/science/article/pii/S0370269318300327?via%3Dihub

  13. Electromagnetic fields with vanishing quantum corrections

    Czech Academy of Sciences Publication Activity Database

    Ortaggio, Marcello; Pravda, Vojtěch

    2018-01-01

    Roč. 779, 10 April (2018), s. 393-395 ISSN 0370-2693 R&D Projects: GA ČR GA13-10042S Institutional support: RVO:67985840 Keywords : nonlinear electrodynamics * quantum corrections Subject RIV: BA - General Mathematics OBOR OECD: Applied mathematics Impact factor: 4.807, year: 2016 https://www. science direct.com/ science /article/pii/S0370269318300327?via%3Dihub

  14. Exact Green's function renormalization approach to spectral properties of open quantum systems driven by harmonically time-dependent fields

    Science.gov (United States)

    Arrachea, Liliana

    2007-01-01

    We present an efficient method and a fast algorithm to exactly calculate spectral functions and one-body observables of open quantum systems described by lattice Hamiltonians with harmonically time-dependent terms and without many-body interactions. The theoretical treatment is based in Keldysh nonequilibrium Green’s function formalism. We illustrate the implementation of the technique in a paradigmatic model of a quantum pump driven by local fields oscillating in time with one and two harmonic components.

  15. Quantum field between moving mirrors: A three dimensional example

    Science.gov (United States)

    Hacyan, S.; Jauregui, Roco; Villarreal, Carlos

    1995-01-01

    The scalar quantum field uniformly moving plates in three dimensional space is studied. Field equations for Dirichlet boundary conditions are solved exactly. Comparison of the resulting wavefunctions with their instantaneous static counterpart is performed via Bogolubov coefficients. Unlike the one dimensional problem, 'particle' creation as well as squeezing may occur. The time dependent Casimir energy is also evaluated.

  16. Indefinite-metric quantum field theory of general relativity, 2

    International Nuclear Information System (INIS)

    Nakanishi, Noboru

    1978-01-01

    The canonical commutation relations are analyzed in detail in the manifestly covariant quantum field theory of general relativity proposed previously. It is explicitly proved that the BRS charge is indeed the generator of the BRS transformation both in the Landau gauge and in the non-Landau one. The equivalence between the field equations and the Heisenberg equations is confirmed. (author)

  17. Deformations of quantum field theories on spacetimes with Killing vector fields

    Energy Technology Data Exchange (ETDEWEB)

    Dappiaggi, Claudio [Hamburg Univ. (Germany). II. Inst. fuer Theoretische Physik; Lechner, Gandalf [Wien Univ. (Austria). Fakultaet fuer Physik; Morfa-Morales, Eric [Erwin Schroedinger Institut fuer Mathematische Physik, Wien (Austria)

    2010-06-15

    The recent construction and analysis of deformations of quantum field theories by warped convolutions is extended to a class of curved spacetimes. These spacetimes carry a family of wedge-like regions which share the essential causal properties of the Poincare transforms of the Rindler wedge in Minkowski space. In the setting of deformed quantum field theories, they play the role of typical localization regions of quantum fields and observables. As a concrete example of such a procedure, the deformation of the free Dirac field is studied. (orig.)

  18. Optimal information transfer in enzymatic networks: A field theoretic formulation

    Science.gov (United States)

    Samanta, Himadri S.; Hinczewski, Michael; Thirumalai, D.

    2017-07-01

    Signaling in enzymatic networks is typically triggered by environmental fluctuations, resulting in a series of stochastic chemical reactions, leading to corruption of the signal by noise. For example, information flow is initiated by binding of extracellular ligands to receptors, which is transmitted through a cascade involving kinase-phosphatase stochastic chemical reactions. For a class of such networks, we develop a general field-theoretic approach to calculate the error in signal transmission as a function of an appropriate control variable. Application of the theory to a simple push-pull network, a module in the kinase-phosphatase cascade, recovers the exact results for error in signal transmission previously obtained using umbral calculus [Hinczewski and Thirumalai, Phys. Rev. X 4, 041017 (2014), 10.1103/PhysRevX.4.041017]. We illustrate the generality of the theory by studying the minimal errors in noise reduction in a reaction cascade with two connected push-pull modules. Such a cascade behaves as an effective three-species network with a pseudointermediate. In this case, optimal information transfer, resulting in the smallest square of the error between the input and output, occurs with a time delay, which is given by the inverse of the decay rate of the pseudointermediate. Surprisingly, in these examples the minimum error computed using simulations that take nonlinearities and discrete nature of molecules into account coincides with the predictions of a linear theory. In contrast, there are substantial deviations between simulations and predictions of the linear theory in error in signal propagation in an enzymatic push-pull network for a certain range of parameters. Inclusion of second-order perturbative corrections shows that differences between simulations and theoretical predictions are minimized. Our study establishes that a field theoretic formulation of stochastic biological signaling offers a systematic way to understand error propagation in

  19. Computer algebra in quantum field theory integration, summation and special functions

    CERN Document Server

    Schneider, Carsten

    2013-01-01

    The book focuses on advanced computer algebra methods and special functions that have striking applications in the context of quantum field theory. It presents the state of the art and new methods for (infinite) multiple sums, multiple integrals, in particular Feynman integrals, difference and differential equations in the format of survey articles. The presented techniques emerge from interdisciplinary fields: mathematics, computer science and theoretical physics; the articles are written by mathematicians and physicists with the goal that both groups can learn from the other field, including

  20. Magnetic-field-dependent optical properties and interdot correlations in coupled quantum dots

    International Nuclear Information System (INIS)

    Bellucci, Devis; Troiani, Filippo; Goldoni, Guido; Molinari, Elisa

    2005-01-01

    We theoretically investigate the properties of neutral and charged excitons in vertically coupled quantum dots, as a function of the in-plane magnetic field. The single-particle states are computed by numerically solving the 3D effective-mass equation, while the neutral- and charged-exciton states are obtained by means of a configuration interaction approach. We show that the field determines an enhancement of the interdot correlations, resulting in unexpected carrier localization. The field effect on the excitonic binding energies is also discussed, and is shown to strongly depend on the charging

  1. BOOK REVIEW: Classical Solutions in Quantum Field Theory Classical Solutions in Quantum Field Theory

    Science.gov (United States)

    Mann, Robert

    2013-02-01

    Quantum field theory has evolved from its early beginnings as a tool for understanding the interaction of light with matter into a rather formidable technical paradigm, one that has successfully provided the mathematical underpinnings of all non-gravitational interactions. Over the eight decades since it was first contemplated the methods have become increasingly more streamlined and sophisticated, yielding new insights into our understanding of the subatomic world and our abilities to make clear and precise predictions. Some of the more elegant methods have to do with non-perturbative and semiclassical approaches to the subject. The chief players here are solitons, instantons, and anomalies. Over the past three decades there has been a steady rise in our understanding of these objects and of our ability to calculate their effects and implications for the rest of quantum field theory. This book is a welcome contribution to this subject. In 12 chapters it provides a clear synthesis of the key developments in these subjects at a level accessible to graduate students that have had an introductory course to quantum field theory. In the author's own words it provides both 'a survey and an overview of this field'. The first half of the book concentrates on solitons--kinks, vortices, and magnetic monopoles--and their implications for the subject. The reader is led first through the simplest models in one spatial dimension, into more sophisticated cases that required more advanced topological methods. The author does quite a nice job of introducing the various concepts as required, and beginning students should be able to get a good grasp of the subject directly from the text without having to first go through the primary literature. The middle part of the book deals with the implications of these solitons for both cosmology and for duality. While the cosmological discussion is quite nice, the discussion on BPS solitons, supersymmetry and duality is rather condensed. It is

  2. Theoretical study of excitonic complexes in semiconductors quantum wells; Estudo teorico de complexos excitonicos em pocos quanticos de semicondutores

    Energy Technology Data Exchange (ETDEWEB)

    Dacal, Luis Carlos Ogando

    2001-08-01

    A physical system where indistinguishable particles interact with each other creates the possibility of studying correlation and exchange effect. The simplest system is that one with only two indistinguishable particles. In condensed matter physics, these complexes are represented by charged excitons, donors and acceptors. In quantum wells, the valence band is not parabolic, therefore, the negatively charged excitons and donors are theoretically described in a simpler way. Despite the fact that the stability of charged excitons (trions) is known since the late 50s, the first experimental observation occurred only at the early 90s in quantum well samples, where their binding energies are one order of magnitude larger due to the one dimensional carriers confinement. After this, these complexes became the subject of an intense research because the intrinsic screening of electrical interactions in semiconductor materials allows that magnetic fields that are usual in laboratories have strong effects on the trion binding energy. Another rich possibility is the study of trions as an intermediate state between the neutral exciton and the Fermi edge singularity when the excess of doping carriers is increased. In this thesis, we present a theoretical study of charged excitons and negatively charged donors in GaAs/Al{sub 0.3}Ga{sub 0.7}As quantum wells considering the effects of external electric and magnetic fields. We use a simple, accurate and physically clear method to describe these systems in contrast with the few and complex treatments s available in the literature. Our results show that the QW interface defects have an important role in the trion dynamics. This is in agreement with some experimental works, but it disagrees with other ones. (author)

  3. Dynamics of plasmonic field polarization induced by quantum coherence in quantum dot-metallic nanoshell structures.

    Science.gov (United States)

    Sadeghi, S M

    2014-09-01

    When a hybrid system consisting of a semiconductor quantum dot and a metallic nanoparticle interacts with a laser field, the plasmonic field of the metallic nanoparticle can be normalized by the quantum coherence generated in the quantum dot. In this Letter, we study the states of polarization of such a coherent-plasmonic field and demonstrate how these states can reveal unique aspects of the collective molecular properties of the hybrid system formed via coherent exciton-plasmon coupling. We show that transition between the molecular states of this system can lead to ultrafast polarization dynamics, including sudden reversal of the sense of variations of the plasmonic field and formation of circular and elliptical polarization.

  4. Noncommutative Geometry, Quantum Fields and Motives

    CERN Document Server

    Connes, Alain

    2007-01-01

    The unifying theme of this book is the interplay among noncommutative geometry, physics, and number theory. The two main objects of investigation are spaces where both the noncommutative and the motivic aspects come to play a role: space-time, where the guiding principle is the problem of developing a quantum theory of gravity, and the space of primes, where one can regard the Riemann Hypothesis as a long-standing problem motivating the development of new geometric tools. The book stresses the relevance of noncommutative geometry in dealing with these two spaces. The first part of the book dea

  5. Field-emission from quantum-dot-in-perovskite solids.

    Science.gov (United States)

    García de Arquer, F Pelayo; Gong, Xiwen; Sabatini, Randy P; Liu, Min; Kim, Gi-Hwan; Sutherland, Brandon R; Voznyy, Oleksandr; Xu, Jixian; Pang, Yuangjie; Hoogland, Sjoerd; Sinton, David; Sargent, Edward

    2017-03-24

    Quantum dot and well architectures are attractive for infrared optoelectronics, and have led to the realization of compelling light sensors. However, they require well-defined passivated interfaces and rapid charge transport, and this has restricted their efficient implementation to costly vacuum-epitaxially grown semiconductors. Here we report solution-processed, sensitive infrared field-emission photodetectors. Using quantum-dots-in-perovskite, we demonstrate the extraction of photocarriers via field emission, followed by the recirculation of photogenerated carriers. We use in operando ultrafast transient spectroscopy to sense bias-dependent photoemission and recapture in field-emission devices. The resultant photodiodes exploit the superior electronic transport properties of organometal halide perovskites, the quantum-size-tuned absorption of the colloidal quantum dots and their matched interface. These field-emission quantum-dot-in-perovskite photodiodes extend the perovskite response into the short-wavelength infrared and achieve measured specific detectivities that exceed 10 12 Jones. The results pave the way towards novel functional photonic devices with applications in photovoltaics and light emission.

  6. Quantum Monte Carlo calculations with chiral effective field theory interactions

    Energy Technology Data Exchange (ETDEWEB)

    Tews, Ingo

    2015-10-12

    The neutron-matter equation of state connects several physical systems over a wide density range, from cold atomic gases in the unitary limit at low densities, to neutron-rich nuclei at intermediate densities, up to neutron stars which reach supranuclear densities in their core. An accurate description of the neutron-matter equation of state is therefore crucial to describe these systems. To calculate the neutron-matter equation of state reliably, precise many-body methods in combination with a systematic theory for nuclear forces are needed. Chiral effective field theory (EFT) is such a theory. It provides a systematic framework for the description of low-energy hadronic interactions and enables calculations with controlled theoretical uncertainties. Chiral EFT makes use of a momentum-space expansion of nuclear forces based on the symmetries of Quantum Chromodynamics, which is the fundamental theory of strong interactions. In chiral EFT, the description of nuclear forces can be systematically improved by going to higher orders in the chiral expansion. On the other hand, continuum Quantum Monte Carlo (QMC) methods are among the most precise many-body methods available to study strongly interacting systems at finite densities. They treat the Schroedinger equation as a diffusion equation in imaginary time and project out the ground-state wave function of the system starting from a trial wave function by propagating the system in imaginary time. To perform this propagation, continuum QMC methods require as input local interactions. However, chiral EFT, which is naturally formulated in momentum space, contains several sources of nonlocality. In this Thesis, we show how to construct local chiral two-nucleon (NN) and three-nucleon (3N) interactions and discuss results of first QMC calculations for pure neutron systems. We have performed systematic auxiliary-field diffusion Monte Carlo (AFDMC) calculations for neutron matter using local chiral NN interactions. By

  7. How do ligands influence the quantum yields of cyclometalated platinum(ii) complexes, a theoretical research study.

    Science.gov (United States)

    Yang, Baozhu; Huang, Shuang; Wang, Jianhao

    2017-08-30

    A series of cyclometalated platinum(ii) complexes have been investigated with the TDDFT method. These complexes have similar structures but distinct phosphorescence quantum yields. Theoretical calculations were carried out to explain the differences in quantum yields from the conjugation effect of the cyclometalated ligand, molecular rigidity and ligand-field strength of the monodentate ligand. The radiative decay rate constants (k r ) have been discussed with the oscillator strength (f n ), the strength of the spin-orbit coupling (SOC) interaction between the lowest energy triplet excited state (T 1 ) and singlet excited states (S n ), and the energy gaps between E(T 1 ) and E(S n ). To illustrate the nonradiative decay processes, the transition states (TS) between the triplet metal-centered state ( 3 MC) and T 1 states have been optimized. In addition, the minimum energy crossing points (MECPs) between 3 MC and the ground states (S 0 ) were optimized. Finally, the potential energy curves along the nonradiative decay pathways are simulated. To obtain a phosphorescent complex with a high quantum yield, the complex should retain molecular rigidity well in the S 1 and T 1 states, while showing significant structural distortion at the MECP structure.

  8. Einstein causal quantum fields on lattices with discrete Lorentz invariance

    International Nuclear Information System (INIS)

    Baumgaertel, H.

    1986-01-01

    Results on rigorous construction of quantum fields on the hypercubic lattice Z 4 considered as a lattice in the Minkowski space R 4 are presented. Two associated fields are constructed: The first one having on the lattice points of Z 4 is causal and Poincare invariant in the discrete sense. The second one is an interpolating field over R 4 which is pointlike, translationally covariant and spectral in such a manner that the 'real' lattices field is the restriction of the interpolating field to Z 4 . Furthermore, results on a rigorous perturbation theory of such fields are mentioned

  9. Noncommutative gravity and quantum field theory on noncummutative curved spacetimes

    International Nuclear Information System (INIS)

    Schenkel, Alexander

    2011-01-01

    The purpose of the first part of this thesis is to understand symmetry reduction in noncommutative gravity, which then allows us to find exact solutions of the noncommutative Einstein equations. We propose an extension of the usual symmetry reduction procedure, which is frequently applied to the construction of exact solutions of Einstein's field equations, to noncommutative gravity and show that this leads to preferred choices of noncommutative deformations of a given symmetric system. We classify in the case of abelian Drinfel'd twists all consistent deformations of spatially flat Friedmann-Robertson-Walker cosmologies and of the Schwarzschild black hole. The deformed symmetry structure allows us to obtain exact solutions of the noncommutative Einstein equations in many of our models, for which the noncommutative metric field coincides with the classical one. In the second part we focus on quantum field theory on noncommutative curved spacetimes. We develop a new formalism by combining methods from the algebraic approach to quantum field theory with noncommutative differential geometry. The result is an algebra of observables for scalar quantum field theories on a large class of noncommutative curved spacetimes. A precise relation to the algebra of observables of the corresponding undeformed quantum field theory is established. We focus on explicit examples of deformed wave operators and find that there can be noncommutative corrections even on the level of free field theories, which is not the case in the simplest example of the Moyal-Weyl deformed Minkowski spacetime. The convergent deformation of simple toy-models is investigated and it is shown that these quantum field theories have many new features compared to formal deformation quantization. In addition to the expected nonlocality, we obtain that the relation between the deformed and the undeformed quantum field theory is affected in a nontrivial way, leading to an improved behavior of the noncommutative

  10. Noncommutative gravity and quantum field theory on noncummutative curved spacetimes

    Energy Technology Data Exchange (ETDEWEB)

    Schenkel, Alexander

    2011-10-24

    The purpose of the first part of this thesis is to understand symmetry reduction in noncommutative gravity, which then allows us to find exact solutions of the noncommutative Einstein equations. We propose an extension of the usual symmetry reduction procedure, which is frequently applied to the construction of exact solutions of Einstein's field equations, to noncommutative gravity and show that this leads to preferred choices of noncommutative deformations of a given symmetric system. We classify in the case of abelian Drinfel'd twists all consistent deformations of spatially flat Friedmann-Robertson-Walker cosmologies and of the Schwarzschild black hole. The deformed symmetry structure allows us to obtain exact solutions of the noncommutative Einstein equations in many of our models, for which the noncommutative metric field coincides with the classical one. In the second part we focus on quantum field theory on noncommutative curved spacetimes. We develop a new formalism by combining methods from the algebraic approach to quantum field theory with noncommutative differential geometry. The result is an algebra of observables for scalar quantum field theories on a large class of noncommutative curved spacetimes. A precise relation to the algebra of observables of the corresponding undeformed quantum field theory is established. We focus on explicit examples of deformed wave operators and find that there can be noncommutative corrections even on the level of free field theories, which is not the case in the simplest example of the Moyal-Weyl deformed Minkowski spacetime. The convergent deformation of simple toy-models is investigated and it is shown that these quantum field theories have many new features compared to formal deformation quantization. In addition to the expected nonlocality, we obtain that the relation between the deformed and the undeformed quantum field theory is affected in a nontrivial way, leading to an improved behavior of the

  11. On the cluster propagator in quantum field theory

    International Nuclear Information System (INIS)

    Mogilevskij, O.A.

    1983-01-01

    The problem is discussed whether it is possible to describe the multiple production processes within the framework of nonlocal quantum field theory. The interaction between the cluster field and the field of scalar particles is introduced. By means of summing up a definite class of Feynman diagrams the cluster propagator with the decreasing imaginary part containing the information about the hadron mass spectrum is obtained

  12. Theoretical femtosecond physics atoms and molecules in strong laser fields

    CERN Document Server

    Grossmann, Frank

    2018-01-01

    This textbook extends from the basics of femtosecond physics all the way to some of the latest developments in the field. In this updated edition, the chapter on laser-driven atoms is augmented by the discussion of two-electron atoms interacting with strong and short laser pulses, as well as by a review of ATI rings and low energy structures in photo-electron spectra. In the chapter on laser-driven molecules a discussion of 2D infrared spectroscopy is incorporated. Theoretical investigations of atoms and molecules interacting with pulsed lasers up to atomic field strengths on the order of 10^16 W/cm² are leading to an understanding of many challenging experimental discoveries. The presentation starts with a brief introduction to pulsed laser physics. The basis for the non-perturbative treatment of laser-matter interaction in the book is the time-dependent Schrödinger equation. Its analytical as well as numerical solution are laid out in some detail. The light field is treated classically and different possi...

  13. Monte Carlo field-theoretic simulations of a homopolymer blend

    Science.gov (United States)

    Spencer, Russell; Matsen, Mark

    Fluctuation corrections to the macrophase segregation transition (MST) in a symmetric homopolymer blend are examined using Monte Carlo field-theoretic simulations (MC-FTS). This technique involves treating interactions between unlike monomers using standard Monte-Carlo techniques, while enforcing incompressibility as is done in mean-field theory. When using MC-FTS, we need to account for a UV divergence. This is done by renormalizing the Flory-Huggins interaction parameter to incorporate the divergent part of the Hamiltonian. We compare different ways of calculating this effective interaction parameter. Near the MST, the length scale of compositional fluctuations becomes large, however, the high computational requirements of MC-FTS restrict us to small system sizes. We account for these finite size effects using the method of Binder cumulants, allowing us to locate the MST with high precision. We examine fluctuation corrections to the mean field MST, χN = 2 , as they vary with the invariant degree of polymerization, N =ρ2a6 N . These results are compared with particle-based simulations as well as analytical calculations using the renormalized one loop theory. This research was funded by the Center for Sustainable Polymers.

  14. Quantum Prisoners' Dilemma in Fluctuating Massless Scalar Field

    Science.gov (United States)

    Huang, Zhiming

    2017-12-01

    Quantum systems are easily affected by external environment. In this paper, we investigate the influences of external massless scalar field to quantum Prisoners' Dilemma (QPD) game. We firstly derive the master equation that describes the system evolution with initial maximally entangled state. Then, we discuss the effects of a fluctuating massless scalar field on the game's properties such as payoff, Nash equilibrium, and symmetry. We find that for different game strategies, vacuum fluctuation has different effects on payoff. Nash equilibrium is broken but the symmetry of the game is not violated.

  15. Electric field engineering using quantum-size-effect-tuned heterojunctions

    KAUST Repository

    Adinolfi, V.

    2013-07-03

    A quantum junction solar cell architecture was recently reported that employs colloidal quantum dots (CQDs) on each side of the p-n junction. This architecture extends the range of design opportunities for CQD photovoltaics, since the bandgap can be tuned across the light-absorbing semiconductor layer via control over CQD size, employing solution-processed, room-temperature fabricated materials. We exploit this feature by designing and demonstrating a field-enhanced heterojunction architecture. We optimize the electric field profile within the solar cell through bandgap engineering, thereby improving carrier collection and achieving an increased open circuit voltage, resulting in a 12% improvement in power conversion efficiency.

  16. Effects of a scalar scaling field on quantum mechanics

    Science.gov (United States)

    Benioff, Paul

    2016-07-01

    This paper describes the effects of a complex scalar scaling field on quantum mechanics. The field origin is an extension of the gauge freedom for basis choice in gauge theories to the underlying scalar field. The extension is based on the idea that the value of a number at one space time point does not determine the value at another point. This, combined with the description of mathematical systems as structures of different types, results in the presence of separate number fields and vector spaces as structures, at different space time locations. Complex number structures and vector spaces at each location are scaled by a complex space time dependent scaling factor. The effect of this scaling factor on several physical and geometric quantities has been described in other work. Here the emphasis is on quantum mechanics of one and two particles, their states and properties. Multiparticle states are also briefly described. The effect shows as a complex, nonunitary, scalar field connection on a fiber bundle description of nonrelativistic quantum mechanics. The lack of physical evidence for the presence of this field so far means that the coupling constant of this field to fermions is very small. It also means that the gradient of the field must be very small in a local region of cosmological space and time. Outside this region, there are no restrictions on the field gradient.

  17. Renormalization Group in different fields of theoretical physics

    International Nuclear Information System (INIS)

    Shirkov, D.V.

    1992-02-01

    A very simple and general approach to the symmetry that is widely known as a Renormalization Group symmetry is presented. It essentially uses a functional formulation of group transformations that can be considered as a generalization of self-similarity transformations well known in mathematical physics since last century. This generalized Functional Self-Similarity symmetry and corresponding group transformations are discussed first for a number of simple physical problems taken from diverse fields of classical physics as well as for QED. Then we formulate the Renorm-Group Method as a regular procedure that essentially improves the approximate solutions near the singularity. After that we discuss relations between different formulations of Renormalization Group as they appear in various parts of a modern theoretical physics. Finally we present several topics of RGM application in modern QFT. (author)

  18. Theoretical Advanced Study Institute in Elementary Particle Physics: New Frontiers in Fields and Strings

    CERN Document Server

    Vieira, Pedro; DeWolfe, Oliver

    2017-01-01

    The program will consist of a pedagogical series of lectures and seminars. Lectures will be given over a four-week period, three or four lectures per day, Monday through Friday. The audience will be composed primarily of advanced theoretical graduate students. Experimentalists with a strong background in theory are also encouraged to apply. Some post-doctoral fellows will be admitted, but preference will be given to applicants who will not have received their Ph.D. before 2015. The minimum background needed to get full benefit of TASI is a knowledge of quantum field theory (including RGEs) and familiarity with the Standard Model. Some familiarity with SUSY and string theory would be helpful. We hope to provide some subsidy, but students will need partial support from other sources. Rooms, meals, and access to all facilities will be provided at reasonable rates in beautifully located dormitories at the University of Colorado.

  19. Axiomatic approach to perturbative quantum field teory

    Energy Technology Data Exchange (ETDEWEB)

    Steinmann, O. [Bielefeld Univ. (Germany). Fakultaet fuer Physik

    1995-10-01

    A derivation with axiomatic methods of a perturbative expansion for the Wightman functions of a relativistic field theory is described. The method gives also the correlation functions of the fields in KMS states. Using these results, a scattering formalism for QED is introduced, which does not involve any infrared divergent quantities. (orig.).

  20. Fractional Quantum Field Theory: From Lattice to Continuum

    Directory of Open Access Journals (Sweden)

    Vasily E. Tarasov

    2014-01-01

    Full Text Available An approach to formulate fractional field theories on unbounded lattice space-time is suggested. A fractional-order analog of the lattice quantum field theories is considered. Lattice analogs of the fractional-order 4-dimensional differential operators are proposed. We prove that continuum limit of the suggested lattice field theory gives a fractional field theory for the continuum 4-dimensional space-time. The fractional field equations, which are derived from equations for lattice space-time with long-range properties of power-law type, contain the Riesz type derivatives on noninteger orders with respect to space-time coordinates.

  1. Introduction to a Quantum Theory over a Galois Field

    Directory of Open Access Journals (Sweden)

    Felix M. Lev

    2010-11-01

    Full Text Available We consider a quantum theory based on a Galois field. In this approach infinities cannot exist, the cosmological constant problem does not arise, and one irreducible representation (IR of the symmetry algebra splits into independent IRs describing a particle an its antiparticle only in the approximation when de Sitter energies are much less than the characteristic of the field. As a consequence, the very notions of particles and antiparticles are only approximate and such additive quantum numbers as the electric, baryon and lepton charges are conserved only in this approximation. There can be no neutral elementary particles and the spin-statistics theorem can be treated simply as a requirement that standard quantum theory should be based on complex numbers.

  2. Cosmological applications of algebraic quantum field theory in curved spacetimes

    CERN Document Server

    Hack, Thomas-Paul

    2016-01-01

    This book provides a largely self-contained and broadly accessible exposition on two cosmological applications of algebraic quantum field theory (QFT) in curved spacetime: a fundamental analysis of the cosmological evolution according to the Standard Model of Cosmology; and a fundamental study of the perturbations in inflation. The two central sections of the book dealing with these applications are preceded by sections providing a pedagogical introduction to the subject. Introductory material on the construction of linear QFTs on general curved spacetimes with and without gauge symmetry in the algebraic approach, physically meaningful quantum states on general curved spacetimes, and the backreaction of quantum fields in curved spacetimes via the semiclassical Einstein equation is also given. The reader should have a basic understanding of General Relativity and QFT on Minkowski spacetime, but no background in QFT on curved spacetimes or the algebraic approach to QFT is required.

  3. Classical and Quantum Chaos in a quantum dot in time-periodic magnetic fields

    OpenAIRE

    Badrinarayanan, R.; José, Jorge V.

    1996-01-01

    We investigate the classical and quantum dynamics of an electron confined to a circular quantum dot in the presence of homogeneous $B_{dc}+B_{ac}$ magnetic fields. The classical motion shows a transition to chaotic behavior depending on the ratio $\\epsilon=B_{ac}/B_{dc}$ of field magnitudes and the cyclotron frequency ${\\tilde\\omega_c}$ in units of the drive frequency. We determine a phase boundary between regular and chaotic classical behavior in the $\\epsilon$ vs ${\\tilde\\omega_c}$ plane. I...

  4. Theoretical femtosecond physics atoms and molecules in strong laser fields

    CERN Document Server

    Grossmann, Frank

    2013-01-01

    Theoretical investigations of atoms and molecules interacting with pulsed or continuous wave lasers up to atomic field strengths on the order of 10^16 W/cm² are leading to an understanding of many challenging experimental discoveries. This book deals with the basics of femtosecond physics and goes up to the latest applications of new phenomena. The book presents an introduction to laser physics with mode-locking and pulsed laser operation. The solution of the time-dependent Schrödinger equation is discussed both analytically and numerically. The basis for the non-perturbative treatment of laser-matter interaction in the book is the numerical solution of the time-dependent Schrödinger equation. The light field is treated classically, and different possible gauges are discussed. Physical phenonema, ranging from Rabi-oscillations in two-level systems to the ionization of atoms, the generation of high harmonics, the ionization and dissociation of molecules as well as the control of chemical reactions are pre...

  5. On relativistic irreducible quantum fields fulfilling CCR

    International Nuclear Information System (INIS)

    Baumann, K.

    1987-01-01

    Let phi be a relativistic scalar field fulfilling canonical commutation relations (CCR). Furthermore it is assumed that the time zero fields and momenta form an irreducible set. Based on estimates given by Herbst [I. W. Herbst, J. Math. Phys. 17, 1210 (1976)], and by methods developed by Powers [R. T. Powers, Commun. Math. Phys. 4, 145 (1967)], it is shown that phi has to be a free field in n>3 space dimensions. For n = 3 (resp. n = 2) restrictions that look similar to the restriction in a formal :phi 4 : 3 /sub +/ 1 (resp. :phi 6 : 2 /sub +/ 1 ) theory are obtained

  6. Quantum field theory approaches to meson structure

    International Nuclear Information System (INIS)

    Branz, Tanja

    2011-01-01

    Meson spectroscopy became one of the most interesting topics in particle physics in the last ten years. In particular, the discovery of new unexpected states in the charmonium spectrum which cannot be simply explained by the constituent quark model attracted the interest of many theoretical efforts. In the present thesis we discuss different meson structures ranging from light and heavy quark-antiquark states to bound states of hadrons-hadronic molecules. Here we consider the light scalar mesons f 0 (980) and a 0 (980) and the charmonium-like Y(3940), Y(4140) and Z ± (4430) states. In the discussion of the meson properties like mass spectrum, total and partial decay widths and production rates we introduce three different theoretical methods for the treatment and description of hadronic structure. For the study of bound states of mesons we apply a coupled channel approach which allows for the dynamical generation of meson-meson resonances. The decay properties of meson molecules are further on studied within a second model based on effective Lagrangians describing the interaction of the bound state and its constituents. Besides hadronic molecules the effective Lagrangian approach is also used to study the radiative and strong decay properties of ordinary quark-antiquark (q anti q) states. The AdS/QCD model forms the completion of the three theoretical methods introduced in the present thesis. This holographic model provides a completely different ansatz and is based on extra dimensions and string theory. Within this framework we calculate the mass spectrum of light and heavy mesons and their decay constants.

  7. A Modern Introduction to Quantum Field Theory (Oxford Master Series in Physics)

    Energy Technology Data Exchange (ETDEWEB)

    Straumann, N [Universitaet Zuerich (Switzerland)

    2005-06-21

    This new book on quantum field theory by Michele Maggiore fits well into the Oxford Master Series in Physics, which is designed for final year undergraduate and beginning graduate students in physics. It is based on the teaching experience of the author with students in the fourth year at the University of Geneva. In this sense it is a two-semester course book for students exposed to quantum field theory for the first time. Maggiore gives, on slightly less than 300 pages, a balanced introduction to a vast field of twentieth century physics that will help students going on to study more advanced and specialized courses. Beside applications to many processes in particle physics that can also be found in many other textbooks, the author emphasizes conceptual, structural and methodological aspects of quantum field theory. After an introductory chapter, the group theoretical tools required to implement Lorentz invariance in quantum field theory are developed on 30 pages. Chapter 3 is devoted to classical field theory, emphasizing symmetries and conservation laws. The quantization of free fields in the next chapter follows traditional lines. Here one may miss a section describing the mathematical structure of the Fock space. It is also not said that in infinite dimensions von Neumann's uniqueness theorem for the representations of the canonical commutation relations no longer holds. The operations C, P, T are carefully discussed. In the relatively long chapter 5, perturbation theory and renormalization are developed. In this context the author discusses the modern view on renormalizability, and also emphasizes in a separate section the seriousness of the cosmological constant problem in quantum field theory. The next three chapters provide applications of the theory, especially to quantum electrodynamics and the low-energy limit of the electroweak theory. Chapters 9, 10, and 11 are meant as a bridge to more advanced courses. In these, path integral quantization, non

  8. Causality in finite temperature quantum field theory

    International Nuclear Information System (INIS)

    Paz, J.P.

    1991-01-01

    Some properties of various 'real time' formalisms are examined. The authors discuss conceptual (and sometimes very important) differences between the Niemi-Semmenoff method, the Closed Time Path formalism, and Thermo Field Dynamics. (author). 15 refs

  9. Conformal invariance in the quantum field theory

    International Nuclear Information System (INIS)

    Kurak, V.

    1975-09-01

    Basic features concerning the present knowledge of conformal symmetry are illustrated in a simple model. Composite field dimensions of this model are computed and related to the conformal group. (author) [pt

  10. Manipulating novel quantum phenomena using synthetic gauge fields

    Science.gov (United States)

    Zhang, Shao-Liang; Zhou, Qi

    2017-11-01

    The past few years have seen fascinating progress in the creation and utilization of synthetic gauge fields for charge-neutral ultracold atoms. Whereas the synthesis of gauge fields in itself is readily interesting, it is more exciting to explore the new era that will be brought by the interplay between synthetic gauge fields and many other degrees of freedom of highly tunable ultracold atoms. This topical review surveys recent developments in using synthetic gauge fields to manipulate novel quantum phenomena that are not easy to access in other systems. We first summarize current experimental methods of creating synthetic gauge fields, including the use of Raman schemes, shaken lattices, and Raman-dressed lattices. We then discuss how synthetic gauge fields bring new physics to non-interacting systems, including degenerate single-particle ground states, quartic dispersions, topological band structures in lattices, and synthetic dimensions. As for interacting systems, we focus on novel quantum many-body states and quantum macroscopic phenomena induced by interactions in the presence of unconventional single-particle dispersions. For bosons, we discuss how a quartic dispersion leads to non-condensed bosonic states at low temperatures and at the ground state. For fermions, we discuss chiral superfluids in the presence of attractive s-wave interaction, where high partial-wave interactions are not required. Finally, we discuss the challenges in current experiments, and conclude with an outlook for what new exciting developments synthetic gauge fields may bring us in the near future.

  11. Effective action for a quantum scalar field in warped spaces

    Energy Technology Data Exchange (ETDEWEB)

    Hoff da Silva, J.M.; Mendonca, E.L.; Scatena, E. [Universidade Estadual Paulista ' ' Julio de Mesquita Filho' ' -UNESP, Departamento de Fisica e Quimica, Guaratingueta, SP (Brazil)

    2015-11-15

    We investigate the one-loop corrections, at zero as well as finite temperature, of a scalar field taking place in a braneworld motivated warped background. After to reach a well-defined problem, we calculate the effective action with the corresponding quantum corrections to each case. (orig.)

  12. Effective action for a quantum scalar field in warped spaces

    Energy Technology Data Exchange (ETDEWEB)

    Hoff da Silva, J. M., E-mail: hoff@feg.unesp.br; Mendonça, E. L., E-mail: eliasleite@feg.unesp.br; Scatena, E., E-mail: eslley@feg.unesp.br [Departamento de Física e Química, Universidade Estadual Paulista “Júlio de Mesquita Filho”-UNESP, Av. Ariberto Pereira da Cunha 333, Pedregulho, Guaratinguetá, SP (Brazil)

    2015-10-30

    We investigate the one-loop corrections, at zero as well as finite temperature, of a scalar field taking place in a braneworld motivated warped background. After to reach a well-defined problem, we calculate the effective action with the corresponding quantum corrections to each case.

  13. Construction of classical and quantum integrable field models ...

    Indian Academy of Sciences (India)

    85, No. 5. — journal of. November 2015 physics pp. 899–913. Construction of classical and quantum integrable field models unravelling hidden possibilities .... It is interesting to note that the infinite set of conserved quantities associated with an inte- ..... that taking c2 as the Hamiltonian would lead to a NLS-type equation.

  14. Combinatorial Quantum Field Theory and Gluing Formula for Determinants

    NARCIS (Netherlands)

    Reshetikhin, N.; Vertman, B.

    2015-01-01

    We define the combinatorial Dirichlet-to-Neumann operator and establish a gluing formula for determinants of discrete Laplacians using a combinatorial Gaussian quantum field theory. In case of a diagonal inner product on cochains we provide an explicit local expression for the discrete

  15. A conformal field theory description of fractional quantum Hall states

    NARCIS (Netherlands)

    Ardonne, E.

    2002-01-01

    In this thesis, we give a description of fractional quantum Hall states in terms of conformal field theory (CFT). As was known for a long time, the Laughlin states could be written in terms of correlators of chiral vertex operators of a c=1 CFT. It was shown by G. Moore and N. Read that more general

  16. Effective action for a quantum scalar field in warped spaces

    Science.gov (United States)

    Hoff da Silva, J. M.; Mendonça, E. L.; Scatena, E.

    2015-11-01

    We investigate the one-loop corrections, at zero as well as finite temperature, of a scalar field taking place in a braneworld motivated warped background. After to reach a well-defined problem, we calculate the effective action with the corresponding quantum corrections to each case.

  17. A quantum field theory of the extended electron

    Energy Technology Data Exchange (ETDEWEB)

    Salesi, Giovanni [Universita Statale di Catania (Italy). Dipt. di Fisica; Recami, Erasmo [Universita Statale di Bergamo, Dalmine, BG (Italy). Facolta di Ingegneria]|[Universidade Estadual de Campinas, SP (Brazil). Dept. de Matematica Aplicada

    1993-12-01

    In a recent paper, the classical model of Barut and Zanghi (BZ) for the electron spin which interpreted the Zitterbewegung (zbw) motion along helical paths and its quantum version have been investigated by using the language of Clifford algebras. In also doing, a new non-linear Dirac-like equation (NDE) was derived. We want to readdress the whole subject, and complete it, by adopting - for the sake of physical clarity - the ordinary tensorial language. In particular, we re-derive here the NDE for the electron quantum field, show it to be associated with a new conserved probability current, and stress its importance for a quantum field theory of spin 1/2 fermions. Actually, we propose this equation in substitution for the Dirac equation, which comes from the former by averaging over a zbw cycle. We then derive a new equation of motion for the quantum field velocity, which will allow us to regard the electron as an extended object, with a classically intelligible internal structure (thus overcoming some known, long-standing problems). We carefully the solutions of the NDE; with special attention to those implying (at the classical limit) light-like helical motions, since these appear to be the most adequate equations for the electron description, from the kinematical and physical points of view, and do cope with the electron electromagnetic properties (such as Coulomb field and intrinsic magnetic moment). (author). 18 refs.

  18. A quantum field theory of the extended electron

    International Nuclear Information System (INIS)

    Salesi, Giovanni; Recami, Erasmo; Universidade Estadual de Campinas, SP

    1993-12-01

    In a recent paper, the classical model of Barut and Zanghi (BZ) for the electron spin which interpreted the Zitterbewegung (zbw) motion along helical paths and its quantum version have been investigated by using the language of Clifford algebras. In also doing, a new non-linear Dirac-like equation (NDE) was derived. We want to readdress the whole subject, and complete it, by adopting - for the sake of physical clarity - the ordinary tensorial language. In particular, we re-derive here the NDE for the electron quantum field, show it to be associated with a new conserved probability current, and stress its importance for a quantum field theory of spin 1/2 fermions. Actually, we propose this equation in substitution for the Dirac equation, which comes from the former by averaging over a zbw cycle. We then derive a new equation of motion for the quantum field velocity, which will allow us to regard the electron as an extended object, with a classically intelligible internal structure (thus overcoming some known, long-standing problems). We carefully the solutions of the NDE; with special attention to those implying (at the classical limit) light-like helical motions, since these appear to be the most adequate equations for the electron description, from the kinematical and physical points of view, and do cope with the electron electromagnetic properties (such as Coulomb field and intrinsic magnetic moment). (author). 18 refs

  19. Representations of homogeneous quantum Lévy fields

    Indian Academy of Sciences (India)

    A strongly covariant GNS representation for the conditionally positive logarithmic functionals of these states is constructed in the complex Minkowski space in terms of canonical quadruples and isometric representations on the underlying pre-Hilbert field space. This is of much use in constructing quantum stochastic ...

  20. Canonical quantum theory of gravitational field with higher derivatives, 3

    International Nuclear Information System (INIS)

    Kawasaki, Shoichiro; Kimura, Tadahiko

    1983-01-01

    A formulation which is invariant under an additional BRS transformation with nilpotency of order two is presented for the canonical theory of the renormalizable quantum gravity with higher derivatives. The canonical quantization is carried out and various equal time (anti-) commutation relations are derived. The asymptotic fields are reanalyzed. The physical particle contents are just the same as those obtained in previous papers. (author)

  1. Quantum mean-field theory of collective dynamics and tunneling

    International Nuclear Information System (INIS)

    Negele, J.W.; Massachusetts Inst. of Tech., Cambridge

    1981-01-01

    In collaboration with Shimon Levit and Zvi Paltiel, significant progress has been made recently in formulating the quantum many-body problem in terms of an expansion about solutions to time-dependent mean-field equations. The essential ideas, principal results, and illustrative examples will be summarized here. (orig./HSI)

  2. Fractional Spin Fluctuations as a Precursor of Quantum Spin Liquids: Majorana Dynamical Mean-Field Study for the Kitaev Model.

    Science.gov (United States)

    Yoshitake, Junki; Nasu, Joji; Motome, Yukitoshi

    2016-10-07

    Experimental identification of quantum spin liquids remains a challenge, as the pristine nature is to be seen in asymptotically low temperatures. We here theoretically show that the precursor of quantum spin liquids appears in the spin dynamics in the paramagnetic state over a wide temperature range. Using the cluster dynamical mean-field theory and the continuous-time quantum Monte Carlo method, which are newly developed in the Majorana fermion representation, we calculate the dynamical spin structure factor, relaxation rate in nuclear magnetic resonance, and magnetic susceptibility for the honeycomb Kitaev model whose ground state is a canonical example of the quantum spin liquid. We find that dynamical spin correlations show peculiar temperature and frequency dependence even below the temperature where static correlations saturate. The results provide the experimentally accessible symptoms of the fluctuating fractionalized spins evincing the quantum spin liquids.

  3. Quantum field theories in two dimensions collected works of Alexei Zamolodchikov

    CERN Document Server

    Pugai, Yaroslav; Zamolodchikov, Alexander

    2012-01-01

    Volume 1 is a collection of reprinted works of Alexei Zamolodchikov who was a prominent theoretical physicist of his time. It contains his works on conformal field theories, 2D quantum gravity, and Liouville theory. These original contributions of Alexei Zamolodchikov have a profound effect on shaping the fast developing areas of theoretical physics. His ideas are expressed lucidly, such as the recursive relation for conformal blocks and the structure of conformal bootstrap in Liouville theory, including the boundary Liouville theory. These ideas are at the foundation of the subject and they are of great interest to a wide community of physicists and mathematicians working in diverse areas. This volume is a part of the 2-volume collection of remarkable research papers that can be used as an advanced textbook by graduate students specializing in string theory, conformal field theory and integrable models of QFT. It is also highly relevant to experts in these fields. Volume 2 includes Alexei Zamolodchikov's w...

  4. Quantum fields from the Hubble to the Planck scale

    CERN Document Server

    Kachelriess, Michael

    2017-01-01

    This book introduces quantum field theory, together with its most important applications to cosmology and astroparticle physics, in a coherent framework. The path integral approach is employed right from the start, and the use of Green functions and generating functionals is illustrated first in quantum mechanics and then in scalar field theory. Massless spin one and two fields are discussed on an equal footing, and gravity is presented as a gauge theory in close analogy with the Yang-Mills case. Concepts relevant to modern research such as helicity methods, effective theories, decoupling, or the stability of the electroweak vacuum are introduced. Various applications such as topological defects, dark matter, baryogenesis, processes in external gravitational fields, inflation and black holes help students to bridge the gap between undergraduate courses and the research literature.

  5. Kinetic theory of the quantum field system with unstable vacuum

    International Nuclear Information System (INIS)

    Smolyanskij, S.A.; Prozorkevich, A.V.; Skokov, V.V.

    2005-01-01

    The description of quantum field systems with meta-stable vacuum is motivated by studies of many physical problems (η-meson sector of the Witten-Di Vecchia-Veneziano model, disoriented chiral condensate, false vacuum decay in inflation cosmological models, etc.). A nonperturbative approach based on the kinetic description within the framework of the quasiparticle representation is proposed. We restrict ourselves to scalar field theory with self-interaction potential having a nontrivial set of vacuum states. If the vacuum state is not uniquely defined, the quasiparticle definition is introduced by some physical reason. As a result, we obtain the self-consistent system of the kinetic equation for quasiparticle distribution function and the equation of motion for the background field. Two examples - the quantum field system with φ 4 and double-well type potential - are considered

  6. Three-dimensional loop quantum gravity: towards a self-gravitating quantum field theory

    International Nuclear Information System (INIS)

    Noui, Karim

    2007-01-01

    In a companion paper, we have emphasized the role of the Drinfeld double DSU(2) in the context of three-dimensional Riemannian loop quantum gravity coupled to massive spinless point particles. We make use of this result to propose a model for a self-gravitating quantum field theory (massive spinless non-causal scalar field) in three-dimensional Riemannian space. We start by constructing the Fock space of the free self-gravitating field: the vacuum is the unique DSU(2) invariant state, one-particle states correspond to DSU(2) unitary irreducible simple representations and any multi-particles states are obtained as the symmetrized tensor product between simple representations. The associated quantum field is defined by the usual requirement of covariance under DSU(2). Then, we introduce a DSU(2)-invariant self-interacting potential (the obtained model is a group field theory) and explicitly compute the lowest order terms (in the self-interaction coupling constant λ) of the propagator and of the three-point function. Finally, we compute the lowest order quantum gravity corrections (in the Newton constant G) to the propagator and to the three-point function

  7. Generating functionals for quantum field theories with random potentials

    International Nuclear Information System (INIS)

    Jain, Mudit; Vanchurin, Vitaly

    2016-01-01

    We consider generating functionals for computing correlators in quantum field theories with random potentials. Examples of such theories include cosmological systems in context of the string theory landscape (e.g. cosmic inflation) or condensed matter systems with quenched disorder (e.g. spin glass). We use the so-called replica trick to define two different generating functionals for calculating correlators of the quantum fields averaged over a given distribution of random potentials. The first generating functional is appropriate for calculating averaged (in-out) amplitudes and involves a single replica of fields, but the replica limit is taken to an (unphysical) negative one number of fields outside of the path integral. When the number of replicas is doubled the generating functional can also be used for calculating averaged probabilities (squared amplitudes) using the in-in construction. The second generating functional involves an infinite number of replicas, but can be used for calculating both in-out and in-in correlators and the replica limits are taken to only a zero number of fields. We discuss the formalism in details for a single real scalar field, but the generalization to more fields or to different types of fields is straightforward. We work out three examples: one where the mass of scalar field is treated as a random variable and two where the functional form of interactions is random, one described by a Gaussian random field and the other by a Euclidean action in the field configuration space.

  8. Field theory approach to quantum hall effect

    International Nuclear Information System (INIS)

    Cabo, A.; Chaichian, M.

    1990-07-01

    The Fradkin's formulation of statistical field theory is applied to the Coulomb interacting electron gas in a magnetic field. The electrons are confined to a plane in normal 3D-space and also interact with the physical 3D-electromagnetic field. The magnetic translation group (MTG) Ward identities are derived. Using them it is shown that the exact electron propagator is diagonalized in the basis of the wave functions of the free electron in a magnetic field whenever the MTG is unbroken. The general tensor structure of the polarization operator is obtained and used to show that the Chern-Simons action always describes the Hall effect properties of the system. A general proof of the Streda formula for the Hall conductivity is presented. It follows that the coefficient of the Chern-Simons terms in the long-wavelength approximation is exactly given by this relation. Such a formula, expressing the Hall conductivity as a simple derivative, in combination with diagonal form of the full propagator allows to obtain a simple expressions for the filling factor and the Hall conductivity. Indeed, these results, after assuming that the chemical potential lies in a gap of the density of states, lead to the conclusion that the Hall conductivity is given without corrections by σ xy = νe 2 /h where ν is the filling factor. In addition it follows that the filling factor is independent of the magnetic field if the chemical potential remains in the gap. (author). 21 ref, 1 fig

  9. Gauge field condensation in geometric quantum chromodynamics

    International Nuclear Information System (INIS)

    Guendelman, E.I.

    1991-09-01

    In odd number of dimensions, it is possible to construct general covariant gauge theories, where the metric is not an independent variable, but local function of the gauge fields. Starting from standardly defined gauge theory, upon functional integration of some variables, we could end up with such moodels. For models with SU(2) and SU(3) symmetry in three dimensions, gauge field condensation take place in the vacuum, which is nevertheless homogeneous and isotropic up to a gauge transformation, provided the space is flat. Introducing Higgs fields that spontaneously break the gauge symmetry, we get a breakdown of the homogenity and isotropy of the vacuum. Finally, we discuss how some of this ideas can be generalized to four and other even dimensions. (author)

  10. Parametrization-dependence of nonlinear quantum field theories

    International Nuclear Information System (INIS)

    Tyutin, I.

    1982-01-01

    It is shown that in an arbitrary quantum field theory a change of variables (transition to a different parametrization) leads only to a change of the field variables in the renormalized action and in the generating functional for the vertex functions. As a consequence of this it is shown that the beta-functions in two-dimensional chiral theories do not depend on the choice of parametrization. A remark on the uniqueness of the renormalized action concludes the paper

  11. Nonperturbative approach to quantum field theories: phase transitions and confinement

    International Nuclear Information System (INIS)

    Yankielowicz, S.

    1976-08-01

    Lectures are given on a nonperturbative approach to quantum field theories. Phenomena are discussed for which the usual weak coupling perturbative approach in terms of Feynman diagrams is of no assistance. Properties associated with large distance behavior, i.e., phase transitions, low lying spectra, coherent excitations which are presumably built out of the long wave structure of the theory are described. These methods are important for the study of strong coupling field theories and the question of quarks confinement. 25 references

  12. A course on quantum field theory and local observables

    International Nuclear Information System (INIS)

    Schroer, Bert

    1997-03-01

    A monograph on Quantum Field Theory and Local Observables is presented, aiming to unify two presently largely disconnected branches of QFT, as follows: the standard (canonical, functional) approach which is mainly perturbative in the sense of an infinitesimal 'deformation' of free fields; nonperturbative constructions of low-dimensional models as the form factor-bootstrap approach (which for the time being is limited to factorable models in d=1+1 spacetime dimensions) and the non-Lagrangian constructions of conformal chiral QFT's

  13. Spectrally resolved far-fields of terahertz quantum cascade lasers

    OpenAIRE

    Brandstetter, Martin; Schönhuber, Sebastian; Krall, Michael; Kainz, Martin A.; Detz, Hermann; Zederbauer, Tobias; Andrews, Aaron M.; Strasser, Gottfried; Unterrainer, Karl

    2016-01-01

    We demonstrate a convenient and fast method to measure the spectrally resolved far-fields of multimode terahertz quantum cascade lasers by combining a microbolometer focal plane array with an FTIR spectrometer. Far-fields of fundamental TM0 and higher lateral order TM1 modes of multimode Fabry-P\\'erot type lasers have been distinguished, which very well fit to the results obtained by a 3D finite-element simulation. Furthermore, multimode random laser cavities have been investigated, analyzing...

  14. Spin and rotations in Galois field quantum mechanics

    International Nuclear Information System (INIS)

    Chang, Lay Nam; Lewis, Zachary; Minic, Djordje; Takeuchi, Tatsu

    2013-01-01

    We discuss the properties of Galois field quantum mechanics constructed on a vector space over the finite Galois field GF(q). In particular, we look at two-level systems analogous to spin, and discuss how SO(3) rotations could be embodied in such a system. We also consider two-particle ‘spin’ correlations and show that the Clauser–Horne-Shimony–Holt inequality is nonetheless not violated in this model. (paper)

  15. Relativistic quantum mechanics and introduction to field theory

    Energy Technology Data Exchange (ETDEWEB)

    Yndurain, F.J. [Universidad Autonoma de Madrid (Spain). Dept. de Fisica Teorica

    1996-12-01

    The following topics were dealt with: relativistic transformations, the Lorentz group, Klein-Gordon equation, spinless particles, spin 1/2 particles, Dirac particle in a potential, massive spin 1 particles, massless spin 1 particles, relativistic collisions, S matrix, cross sections, decay rates, partial wave analysis, electromagnetic field quantization, interaction of radiation with matter, interactions in quantum field theory and relativistic interactions with classical sources.

  16. Electromagnetic fields with vanishing quantum corrections

    Science.gov (United States)

    Ortaggio, Marcello; Pravda, Vojtěch

    2018-04-01

    We show that a large class of null electromagnetic fields are immune to any modifications of Maxwell's equations in the form of arbitrary powers and derivatives of the field strength. These are thus exact solutions to virtually any generalized classical electrodynamics containing both non-linear terms and higher derivatives, including, e.g., non-linear electrodynamics as well as QED- and string-motivated effective theories. This result holds not only in a flat or (anti-)de Sitter background, but also in a larger subset of Kundt spacetimes, which allow for the presence of aligned gravitational waves and pure radiation.

  17. A gauge quantum field theory of confined quarks and gluons

    International Nuclear Information System (INIS)

    Voelkel, A.H.

    1983-01-01

    A SU(3)-gauge quantum field theory with a quark triplet, an antiquark triplet and a self-conjugate gluon octet as basic fields is investigated. In virtue of a non trivial coupling between the representation of the translation group and the SU(3)-colour charge of the basic fields it is proved: (i) The basic quark, antiquark and gluon fields are confined. (ii) Every statevector of the physical Hilbert space is a SU(3)-colour singlet state. (iii) Poincare invariance holds in the physical Hilbert space. (orig.)

  18. Vibrational spectroscopic and quantum theoretical study of host-guest interactions in clathrates: I. Hofmann type clathrates

    Directory of Open Access Journals (Sweden)

    VLADIMIR M. PETRUSEVSKI

    2000-06-01

    Full Text Available Hofmann type clatharates are host-guest compounds with the general formula M(NH32M'(CN4·2G, in which M(NH32M'(CN4 is the host lattice and G is benzene, the guest molecule. In previous studies, host-guest interactions have been investigated by analyzing the RT and LNT vibrational (infrared, far infrared and Raman spectra of these clathrates. All the observed changes in the vibrational spectra of these clathrates are referred to a host-guest interaction originating from weak hydrogen bonding between the ammonia hydrogen atoms from the host lattice and the p electron cloud of the guest (benzene molecules. In order to obtain an insight into the relative importance of the local crystalline field vs. the anharmonicity effects on the spectroscopic properties of the guest species upon enclathration, as well as to explain the observed band shifts and splittings, several quantum theoretical approaches are proposed.

  19. Quantum field theory with soliton conservation laws

    CERN Document Server

    Schrör, B

    1978-01-01

    Field theories with soliton conservation laws are the most promising candidates for explicitly constructable models. The author exemplifies in the case of the massive Thirring model how the old S matrix bootstrap idea, supplemented with a soliton factorization property, may be used as a systematic starting point for the construction of the S matrix, form factors and (hopefully) correlation functions. (34 refs).

  20. Entanglement entropy in free quantum field theory

    International Nuclear Information System (INIS)

    Casini, H; Huerta, M

    2009-01-01

    In this paper, we first introduce the general methods to calculate the entanglement entropy for free fields, within the Euclidean and the real-time formalisms. Then, we describe the particular examples which have been worked out explicitly in two, three and more dimensions.

  1. Causality and analyticity in quantum fields theory

    International Nuclear Information System (INIS)

    Iagolnitzer, D.

    1992-01-01

    This is a presentation of results on the causal and analytical structure of Green functions and on the collision amplitudes in fields theories, for massive particles of one type, with a positive mass and a zero spin value. (A.B.)

  2. Free field theories of spin-mass trajectories and quantum electrodynamics in the null plane

    International Nuclear Information System (INIS)

    Bart, G.R.; Fenster, S.

    1976-06-01

    The ten generators of the Poincare algebra for quantum electrodynamics and other gauge theories are given in the null plane. The explicit correspondence of their field-theoretic form to the Bacry-Chang group-theoretic form in the free case is pointed out. It is then noticed that the forms are independent of the spin and allow inclusion of charge quantum numbers at will, which indicates that they represent an advantageous free-particle starting point for a hadron theory with positive spin-mass trajectories (SMT) and with interaction. The internal oscillator content is extracted for both gauge theories and dual resonance models. Interactions are cubic and quartic in the fields. In the dual model they encompass the SMT, whereas no straightforward extension to SMT is possible for the manifestly covariant theories. The requirements of a field-theoretic SMT interaction are spelled out in an algebraic form which guarantees Poincare invariance; however no such interaction is yet known. The approach indicates how a realistic spectrum might be achieved without composite hadrons and incorporating full Poincare invariance

  3. Relativistic Many-Body Theory A New Field-Theoretical Approach

    CERN Document Server

    Lindgren, Ingvar

    2011-01-01

    Relativistic Many-Body Theory treats — for the first time — the combination of relativistic atomic many-body theory with quantum-electrodynamics (QED) in a unified manner. This book can be regarded as a continuation of the book by Lindgren and Morrison, Atomic Many-Body Theory (Springer 1986), which deals with the non-relativistic theory of many-electron systems, describing several means of treating the electron correlation to essentially all orders of perturbation theory. The treatment of the present book is based upon quantum-field theory, and demonstrates that when the procedure is carried to all orders of perturbation theory, two-particle systems are fully compatible with the relativistically covariant Bethe-Salpeter equation. This procedure can be applied to arbitrary open-shell systems, in analogy with the standard many-body theory, and it is also applicable to systems with more than two particles. Presently existing theoretical procedures for treating atomic systems are, in several cases, insuffici...

  4. Basic course theoretical physics 5/2. Quantum mechanics - methods and applications. 7. upd. ed.; Grundkurs Theoretische Physik 5/2. Quantenmechanik - Methoden und Anwendungen

    Energy Technology Data Exchange (ETDEWEB)

    Nolting, Wolfgang [Humboldt-Universitaet, Berlin (Germany). Inst. fuer Physik

    2012-07-01

    The favourite basic course theoretical physics covers in seven volumes all for the diploma and bachelor/master curricula decisive fields. Each volume mediates well considerably the theoretic-physical knowledge necessary in each semester. Numerous exercise problems with extended solutions serve for the deepening of the matter. The second part of the fifth volume deals with application and the extension of the concept of quantum mechanics developed in the first part. The present new edition contains some new problems, was worked out, and supplemented. It makes by the two-colour presentation a very distinct and fast access to the subject of teaching.

  5. Aspects of quantum field theory in curved space-time

    Energy Technology Data Exchange (ETDEWEB)

    Fulling, S.A. (Texas A and M Univ., College Station, TX (USA). Dept. of Mathematics)

    1989-01-01

    The theory of quantum fields on curved spacetimes has attracted great attention since the discovery, by Stephen Hawking, of black-hole evaporation. It remains an important subject for the understanding of such contemporary topics as inflationary cosmology, quantum gravity and superstring theory. The topics covered include normal-mode expansions for a general elliptic operator, Fock space, the Casimir effect, the Klein 'paradox', particle definition and particle creation in expanding universes, asymptotic expansion of Green's functions and heat kernels, and renormalization of the stress tensor. (author).

  6. Aspects of quantum field theory in curved space-time

    International Nuclear Information System (INIS)

    Fulling, S.A.

    1989-01-01

    The theory of quantum fields on curved spacetimes has attracted great attention since the discovery, by Stephen Hawking, of black-hole evaporation. It remains an important subject for the understanding of such contemporary topics as inflationary cosmology, quantum gravity and superstring theory. The topics covered include normal-mode expansions for a general elliptic operator, Fock space, the Casimir effect, the Klein 'paradox', particle definition and particle creation in expanding universes, asymptotic expansion of Green's functions and heat kernels, and renormalization of the stress tensor. (author)

  7. Classical and quantum mechanics of non-abelian gauge fields

    International Nuclear Information System (INIS)

    Savvidy, G.K.

    1984-01-01

    Classical and quantum mechanics of non-abelian gauge fields are investigated both with and without spontaneous symmetry breaking. The fundamental subsystem (FS) of Yang-Mills classical mechanics (YMCM) is considered. It is shown to be a Kolmogorov K-system, and hence to have strong statistical properties. Integrable systems are also found, to which in terms of KAM theory Yang-Mills-Higgs classical mechanics (YMHCM) is close. Quantum-mechanical properties of the YM system and their relation to the problem of confinement are discussed. (orig.)

  8. Towards experimental quantum-field tomography with ultracold atoms.

    Science.gov (United States)

    Steffens, A; Friesdorf, M; Langen, T; Rauer, B; Schweigler, T; Hübener, R; Schmiedmayer, J; Riofrío, C A; Eisert, J

    2015-07-03

    The experimental realization of large-scale many-body systems in atomic-optical architectures has seen immense progress in recent years, rendering full tomography tools for state identification inefficient, especially for continuous systems. To work with these emerging physical platforms, new technologies for state identification are required. Here we present first steps towards efficient experimental quantum-field tomography. Our procedure is based on the continuous analogues of matrix-product states, ubiquitous in condensed-matter theory. These states naturally incorporate the locality present in realistic physical settings and are thus prime candidates for describing the physics of locally interacting quantum fields. To experimentally demonstrate the power of our procedure, we quench a one-dimensional Bose gas by a transversal split and use our method for a partial quantum-field reconstruction of the far-from-equilibrium states of this system. We expect our technique to play an important role in future studies of continuous quantum many-body systems.

  9. Quantum optical measurements with undetected photons through vacuum field indistinguishability.

    Science.gov (United States)

    Lee, Sun Kyung; Yoon, Tai Hyun; Cho, Minhaeng

    2017-07-26

    Quantum spectroscopy and imaging with undetected idler photons have been demonstrated by measuring one-photon interference between the corresponding entangled signal fields from two spontaneous parametric down conversion (SPDC) crystals. In this Report, we present a new quantum optical measurement scheme utilizing three SPDC crystals in a cascading arrangement; here, neither the detection of the idler photons which interact with materials of interest nor their conjugate signal photons which do not interact with the sample is required. The coherence of signal beams in a single photon W-type path-entangled state is induced and modulated by indistinguishabilities of the idler beams and crucially the quantum vacuum fields. As a result, the optical properties of materials or objects interacting with the idler beam from the first SPDC crystal can be measured by detecting second-order interference between the signal beams generated by the other two SPDC crystals further down the set-up. This gedankenexperiment illustrates the fundamental importance of vacuum fields in generating an optical tripartite entangled state and thus its crucial role in quantum optical measurements.

  10. The path integral method in quantum field theory

    International Nuclear Information System (INIS)

    Burden, C.J.

    1990-01-01

    Richard Feynman is reputed to have once the that in his whole life he had only ever had two really clever ideas. As it has turned out, these two ideas, the path integral formulation of quantum mechanics and the diagrammatic representation of perturbation theory have become the cornerstone of modern quantum field theory and particle physics. The path integral, first hinted at by Dirac in the thirties but developed fully by Feynman in the late 40's provides us with an alternative, though equivalent, description of quantum mechanics to canonical quantization. It was not until the seventies that it found broad application in quantum field theory (QFT), leading of gauge theories. It has also lead to the invention of non-perturbative techniques such as lattice gauge theory and has revealed an intimate connection between QFT and statistical mechanics. This paper, the author develops the basic of QFT form the path integral formalism and introduce the idea of Feynman diagrams for calculating perturbation expansions. I will concentrate mainly on the example of φ 4 theory since it is probably the simplest example of an interacting field theory, though the methods generalize readily to more sophisticated theories

  11. Quantum Coherence and Random Fields at Mesoscopic Scales

    Energy Technology Data Exchange (ETDEWEB)

    Rosenbaum, Thomas F. [Univ. of Chicago, IL (United States)

    2016-03-01

    We seek to explore and exploit model, disordered and geometrically frustrated magnets where coherent spin clusters stably detach themselves from their surroundings, leading to extreme sensitivity to finite frequency excitations and the ability to encode information. Global changes in either the spin concentration or the quantum tunneling probability via the application of an external magnetic field can tune the relative weights of quantum entanglement and random field effects on the mesoscopic scale. These same parameters can be harnessed to manipulate domain wall dynamics in the ferromagnetic state, with technological possibilities for magnetic information storage. Finally, extensions from quantum ferromagnets to antiferromagnets promise new insights into the physics of quantum fluctuations and effective dimensional reduction. A combination of ac susceptometry, dc magnetometry, noise measurements, hole burning, non-linear Fano experiments, and neutron diffraction as functions of temperature, magnetic field, frequency, excitation amplitude, dipole concentration, and disorder address issues of stability, overlap, coherence, and control. We have been especially interested in probing the evolution of the local order in the progression from spin liquid to spin glass to long-range-ordered magnet.

  12. Two-dimensional quantum electrodynamics as a model in the constructive quantum field theory

    International Nuclear Information System (INIS)

    Ito, K.R.

    1976-01-01

    We investigate two-dimensional quantum electrodynamics((QED) 2 ) type models on the basis of the Hamiltonian formalism of a vector field. The transformation into a sine-Gordon equation is clarified as a generalized mass-shift transformation through canonical linear transformations. (auth.)

  13. DFR Perturbative Quantum Field Theory on Quantum Space Time, and Wick Reduction

    Science.gov (United States)

    Piacitelli, Gherardo

    We discuss the perturbative approach à la Dyson to a quantum field theory with nonlocal self-interaction :φ⋆···⋆φ, according to Doplicher, Fredenhagen and Roberts (DFR). In particular, we show that the Wick reduction of nonlocally time-ordered products of Wick monomials can be performed as usual, and we discuss a very simple Dyson diagram.

  14. Quantum field theory in generalised Snyder spaces

    International Nuclear Information System (INIS)

    Meljanac, S.; Meljanac, D.; Mignemi, S.; Štrajn, R.

    2017-01-01

    We discuss the generalisation of the Snyder model that includes all possible deformations of the Heisenberg algebra compatible with Lorentz invariance and investigate its properties. We calculate perturbatively the law of addition of momenta and the star product in the general case. We also undertake the construction of a scalar field theory on these noncommutative spaces showing that the free theory is equivalent to the commutative one, like in other models of noncommutative QFT.

  15. Quantum field theory in generalised Snyder spaces

    Energy Technology Data Exchange (ETDEWEB)

    Meljanac, S.; Meljanac, D. [Rudjer Bošković Institute, Bijenička cesta 54, 10002 Zagreb (Croatia); Mignemi, S., E-mail: smignemi@unica.it [Dipartimento di Matematica e Informatica, Università di Cagliari, viale Merello 92, 09123 Cagliari (Italy); INFN, Sezione di Cagliari, Cittadella Universitaria, 09042 Monserrato (Italy); Štrajn, R. [Dipartimento di Matematica e Informatica, Università di Cagliari, viale Merello 92, 09123 Cagliari (Italy); INFN, Sezione di Cagliari, Cittadella Universitaria, 09042 Monserrato (Italy)

    2017-05-10

    We discuss the generalisation of the Snyder model that includes all possible deformations of the Heisenberg algebra compatible with Lorentz invariance and investigate its properties. We calculate perturbatively the law of addition of momenta and the star product in the general case. We also undertake the construction of a scalar field theory on these noncommutative spaces showing that the free theory is equivalent to the commutative one, like in other models of noncommutative QFT.

  16. Calculations in external fields in quantum chromodynamics

    International Nuclear Information System (INIS)

    Novikov, V.A.; Shifman, M.A.; Vairshtejn, A.I.; Zakharov, V.I.

    1983-01-01

    The technique of calculation of operator expansion coefficients is reviewed. The main emphasis is put on gluon operators which appear in expansion of n-point functions induced by colourless quark currents. Two convenient schemes are discussed in detail: the abstract operator method and the method based on the Fock-Schwinger gauge for the vacuum gluon field. A large number of instructive examples important from the point of view of physical applications is considered

  17. Quantum Computation and Information From Theory to Experiment

    CERN Document Server

    Imai, Hiroshi

    2006-01-01

    Recently, the field of quantum computation and information has been developing through a fusion of results from various research fields in theoretical and practical areas. This book consists of the reviews of selected topics charterized by great progress and cover the field from theoretical areas to experimental ones. It contains fundamental areas, quantum query complexity, quantum statistical inference, quantum cloning, quantum entanglement, additivity. It treats three types of quantum security system, quantum public key cryptography, quantum key distribution, and quantum steganography. A photonic system is highlighted for the realization of quantum information processing.

  18. Quantum mechanical force field for water with explicit electronic polarization.

    Science.gov (United States)

    Han, Jaebeom; Mazack, Michael J M; Zhang, Peng; Truhlar, Donald G; Gao, Jiali

    2013-08-07

    A quantum mechanical force field (QMFF) for water is described. Unlike traditional approaches that use quantum mechanical results and experimental data to parameterize empirical potential energy functions, the present QMFF uses a quantum mechanical framework to represent intramolecular and intermolecular interactions in an entire condensed-phase system. In particular, the internal energy terms used in molecular mechanics are replaced by a quantum mechanical formalism that naturally includes electronic polarization due to intermolecular interactions and its effects on the force constants of the intramolecular force field. As a quantum mechanical force field, both intermolecular interactions and the Hamiltonian describing the individual molecular fragments can be parameterized to strive for accuracy and computational efficiency. In this work, we introduce a polarizable molecular orbital model Hamiltonian for water and for oxygen- and hydrogen-containing compounds, whereas the electrostatic potential responsible for intermolecular interactions in the liquid and in solution is modeled by a three-point charge representation that realistically reproduces the total molecular dipole moment and the local hybridization contributions. The present QMFF for water, which is called the XP3P (explicit polarization with three-point-charge potential) model, is suitable for modeling both gas-phase clusters and liquid water. The paper demonstrates the performance of the XP3P model for water and proton clusters and the properties of the pure liquid from about 900 × 10(6) self-consistent-field calculations on a periodic system consisting of 267 water molecules. The unusual dipole derivative behavior of water, which is incorrectly modeled in molecular mechanics, is naturally reproduced as a result of an electronic structural treatment of chemical bonding by XP3P. We anticipate that the XP3P model will be useful for studying proton transport in solution and solid phases as well as across

  19. A tunable colloidal quantum dot photo field-effect transistor

    KAUST Repository

    Ghosh, Subir

    2011-01-01

    We fabricate and investigate field-effect transistors in which a light-absorbing photogate modulates the flow of current along the channel. The photogate consists of colloidal quantum dots that efficiently transfer photoelectrons to the channel across a charge-separating (type-II) heterointerface, producing a primary and sustained secondary flow that is terminated via electron back-recombination across the interface. We explore colloidal quantum dot sizes corresponding to bandgaps ranging from 730 to 1475 nm and also investigate various stoichiometries of aluminum-doped ZnO (AZO) channel materials. We investigate the role of trap state energies in both the colloidal quantum dot energy film and the AZO channel. © 2011 American Institute of Physics.

  20. Supersymmetric electroweak baryogenesis, nonequilibrium field theory and quantum Boltzmann equations

    CERN Document Server

    Riotto, Antonio

    1998-01-01

    The closed time-path (CPT) formalism is a powerful Green's function formulation to describe nonequilibrium phenomena in field theory and it leads to a complete nonequilibrium quantum kinetic theory. In this paper we make use of the CPT formalism to write down a set of quantum Boltzmann equations describing the local number density asymmetries of the particles involved in supersymmetric electroweak baryogenesis. These diffusion equations automatically and self-consistently incorporate the CP-violating sources which fuel baryogenesis when transport properties allow the CP-violating charges to diffuse in front of the bubble wall separating the broken from the unbroken phase at the electroweak phase transition. This is a significant improvement with respect to recent approaches where the CP-violating sources are inserted by hand into the diffusion equations. Furthermore, the CP-violating sources and the particle number changing interactions manifest ``memory'' effects which are typical of the quantum transp ort t...

  1. The foliation operator in history quantum field theory

    International Nuclear Information System (INIS)

    Isham, C.J.; Savvidou, K.

    2002-01-01

    As a preliminary to discussing the quantization of the foliation in a history form of general relativity, we show how the discussion in an earlier work [J. Math. Phys. 43, 3053 (2002)] of a history version of free, scalar quantum field theory can be augmented in such a way as to include the quantization of the unit-length, timelike vector that determines a Lorentzian foliation of Minkowski space-time. We employ a Hilbert bundle construction that is motivated by (i) discussing the role of the external Lorentz group in the existing history quantum field theory [J. Math. Phys. 43, 3053 (2002)] and (ii) considering a specific representation of the extended history algebra obtained from the multi-symplectic representation of scalar field theory

  2. Study of interacting fields in a canonical formalism in Heisenberg picture of quantum field theory

    International Nuclear Information System (INIS)

    RANAIVOSON, R.T.R.

    2011-01-01

    In this work, we have made a study on the canonical formalism of the quantum field theory. Our contribution has been the development of a study using the Heisenberg picture. We showed that this approach may be useful for the description of quantum dynamics of interacting fields in bounded states. Our approach is to start from the lagrangian density of a classical theory from which one deduce the classical evolution equations of the fields via Euler-Lagrange equation for fields and establish the expression of conserved quantities characterizing the dynamics using the Noether theorem. Passing to the canonical quantization, fields and quantities characterizing the dynamics become quantum operators and evolution equations become operatorial evolution equations in Heisenberg picture. Expressions of quantum observable are also deduced from the expressions of classical conserved quantities. After, we showed that using the properties of fields operators and quantum states vectors, one can deduce from the operatorial evolution equations, the evolution equations for the wave functions of fermions and the evolution equations of expectation values of boson fields. For the illustration, various studies were conducted: the case of electrodynamics, the case of a general gauge theory and the case of the Standard Model. [fr

  3. Field theoretical approach to magnetically coupled layered superconductors

    International Nuclear Information System (INIS)

    Nandori, I.; Vad, K.; Meszaros, S.; Nagy, S.; Sailer, K.

    2006-01-01

    Complete text of publication follows. High transition temperature superconductors have usually a layered structure. The superconducting layers separated by insulating planes are coupled by magnetic or Josephson coupling. Due to this layered structure the lowest energy topological excitations in these systems are not conducting electrons (which are created from Cooper-pairs) but small supercurrent 'rings' which carrie magnetic flux. These are called vortex type excitations. Vortex dominated properties of magnetically coupled superconducting layered systems have recently been investigated in Ref.[1]. Since the planes are magnetically coupled, the pancake type vortices of single layers can form a Pearl-type vortex stack. However, above a critical temperature, due to the thermal fluctuations, the vortex stack is broken up into a number of pancake vortices of fractional flux. Therefore, this configuration undergoes a phase transition of the Kosterlitz-Thouless- Berezinskii (KTB) type at a layer-dependent critical temperature T KTB (N) = T KTB * (N - 1) / N which is connected with the dissociation of the stack. This result has already been obtained in the literature on the basis of approximative methods, therefore, rigorous renormalization group (RG) analysis has been required to clarify the conjecture. The real space RG study of N = 2 layers discussed in Ref.[1] has been assumed to go beyond the previously used approximations but it is based on some a priori assumption and, hence, it loses its predicting power, and it appeared to be rather difficult to generalize for N > 2 layers. In Refs.[2,3,4,5] we open a new platform to consider the vortex dynamics of magnetically coupled layered systems by constructing a multi-layer sine-Gordon (MLSG) type field theoretical model where the two-dimensional sine-Gordon fields characterizing the layers are coupled by an appropriate general mass matrix. The action of the MLSG model reads as S = ∫ d 2 x [1/2 Σ n=1 N (∂ μ φ n ) 2

  4. Keldysh field theory for driven open quantum systems.

    Science.gov (United States)

    Sieberer, L M; Buchhold, M; Diehl, S

    2016-09-01

    Recent experimental developments in diverse areas-ranging from cold atomic gases to light-driven semiconductors to microcavity arrays-move systems into the focus which are located on the interface of quantum optics, many-body physics and statistical mechanics. They share in common that coherent and driven-dissipative quantum dynamics occur on an equal footing, creating genuine non-equilibrium scenarios without immediate counterpart in equilibrium condensed matter physics. This concerns both their non-thermal stationary states and their many-body time evolution. It is a challenge to theory to identify novel instances of universal emergent macroscopic phenomena, which are tied unambiguously and in an observable way to the microscopic drive conditions. In this review, we discuss some recent results in this direction. Moreover, we provide a systematic introduction to the open system Keldysh functional integral approach, which is the proper technical tool to accomplish a merger of quantum optics and many-body physics, and leverages the power of modern quantum field theory to driven open quantum systems.

  5. Democracy of internal symmetries in supersymmetrical quantum field theory

    Energy Technology Data Exchange (ETDEWEB)

    Lopuszanski, J.T.

    1981-12-01

    The freedom of choice of some discrete and internal symmetries in the supersymmetric, massive, interacting quantum field theory is discussed. It is shown that the discrete symmetry consisting of changing the sign of some (not all) scalar fields is incompatible with the supersymmetric structure of the theory. It is further demonstrated that an internal symmetry which transforms only some of the fields of fixed spin leaving the other fields invariant and which acts nontrivially on the supercharges can not be admitted as a symmetry; although it can be a good internal symmetry in absence of supersymmetric covariance. Moreover, in case of a model consisting of scalar, spinor and vector fields even a symmetry which transforms all of the scalar (vector) fields leaving spinor and vector (scalar) fields unaffected is ruled out provided it acts nontrivially on some of the supercharges.

  6. String-localized quantum fields and modular localization

    Energy Technology Data Exchange (ETDEWEB)

    Mund, J. [Juiz de Fora Univ., MG (Brazil). Dept. de Fisica; Schroer, B. [FU-Berlin, Berlin (Germany). Inst. fuer Theoretische Physik; Yngvason, J. [Erwin Schroedinger Institute for Mathematical Physics, Vienna (Austria)

    2005-12-15

    We study free, covariant, quantum (Bose) fields that are associated with irreducible representations of the Poincare group and localized in semi-infinite strings extending to spacelike infinity. Among these are fields that generate the irreducible representations of mass zero and infinite spin that are known to be incompatible with point-like localized fields. For the massive representation and the massless representations of finite helicity, all string-localized free fields can be written as an integral, along the string, of point-localized tensor or spinor fields. As a special case we discuss the string-localized vector fields associated with the point-like electromagnetic field and their relation to the axial gauge condition in the usual setting. (author)

  7. String-localized quantum fields and modular localization

    International Nuclear Information System (INIS)

    Mund, J.

    2005-12-01

    We study free, covariant, quantum (Bose) fields that are associated with irreducible representations of the Poincare group and localized in semi-infinite strings extending to spacelike infinity. Among these are fields that generate the irreducible representations of mass zero and infinite spin that are known to be incompatible with point-like localized fields. For the massive representation and the massless representations of finite helicity, all string-localized free fields can be written as an integral, along the string, of point-localized tensor or spinor fields. As a special case we discuss the string-localized vector fields associated with the point-like electromagnetic field and their relation to the axial gauge condition in the usual setting. (author)

  8. Quantum field theory II: quantum electrodynamics. A bridge between mathematicians and physicists

    International Nuclear Information System (INIS)

    Zeidler, Eberhard

    2009-01-01

    This is the second volume of a modern introduction to quantum field theory which addresses both mathematicians and physicists ranging from advanced undergraduate students to professional scientists. This book seeks to bridge the existing gap between the different languages used by mathematicians and physicists. For students of mathematics it is shown that detailed knowledge of the physical background helps to discover interesting interrelationships between quite diverse mathematical topics. For students of physics fairly advanced mathematics, beyond that included in the usual curriculum in physics, is presented. The present volume concerns a detailed study of the mathematical and physical aspects of the quantum theory of light. (orig.)

  9. Quantum field theory and nuclear structure

    International Nuclear Information System (INIS)

    Celenza, L.S.; Goulard, B.; Shakin, C.M.

    1981-01-01

    We discuss recent successful calculations of the properties of nuclear matter within the context of theories exhibiting mass generation through spontaneous symmetry breaking. We start with the sigma model of Gell-Mann and Levy and introduce the nucleon mass (in a vacuum) in the usual manner. We relate the expectation value of the sigma field in a vacuum to a finite value of the scalar density. If the vacuum is now filled with nucleons (nuclear matter) the scalar density is increased and the new value for the nucleon mass must be determined. We exhibit the equation whose solution determines the new mass, and we also define a perturbative scheme for the determination of this mass. This scheme involves an expansion of the various quantities of the theory in terms of matrix elements calculated with positive- and negative-energy spinors parametrized with the vacuum mass. Although the decrease in the mass upon going from vacuum to nuclear matter at the equilibrium density is quite large (approx.400 MeV), we are still able to exhibit a small parameter which allows for a perturbative expansion of the binding energy and other observables. The leading term in such an expansion reproduces the approximation widely used in other calculations of the properties of nuclear matter. The truncation of the expansion at the leading term is inadequate and this fact accounts for the lack of success in previous calculations using the standard formalism. We proceed to make a transformation to the Weinberg Lagrangian retaining the fluctuating parts of the sigma field. We further make a small-oscillation approximation, dropping the nonlinear terms in this Lagrangian

  10. Relativistic local quantum field theory for m=0 particles

    International Nuclear Information System (INIS)

    Morales Villasevil, A.

    1965-01-01

    A method is introduced ta deal with relativistic quantum field theory for particles with m=0. Two mappings I and J, giving rise respectively to particle and anti particle states, are defined between a test space and the physical Hilbert space. The intrinsic field operator is then defined as the minimal causal linear combinations of operators belonging to the annihilation-creation algebra associated to the germ and antigerm parts of the element. Local elements are introduced as improper test elements and local field operators are constructed in the same way as the intrinsic ones. Commutation rules are given. (Author) 17 refs

  11. Anomalous quantum numbers and topological properties of field theories

    International Nuclear Information System (INIS)

    Polychronakos, A.P.

    1987-01-01

    We examine the connection between anomalous quantum numbers, symmetry breaking patterns and topological properties of some field theories. The main results are the following: In three dimensions the vacuum in the presence of abelian magnetic field configurations behaves like a superconductor. Its quantum numbers are exactly calculable and are connected with the Atiyah-Patodi-Singer index theorem. Boundary conditions, however, play a nontrivial role in this case. Local conditions were found to be physically preferable than the usual global ones. Due to topological reasons, only theories for which the gauge invariant photon mass in three dimensions obeys a quantization condition can support states of nonzero magnetic flux. For similar reasons, this mass induces anomalous angular momentum quantum numbers to the states of the theory. Parity invariance and global flavor symmetry were shown to be incompatible in such theories. In the presence of mass less flavored fermions, parity will always break for an odd number of fermion flavors, while for even fermion flavors it may not break but only at the expense of maximally breaking the flavor symmetry. Finally, a connection between these theories and the quantum Hall effect was indicated

  12. Quantum gravity with matter and group field theory

    International Nuclear Information System (INIS)

    Krasnov, Kirill

    2007-01-01

    A generalization of the matrix model idea to quantum gravity in three and higher dimensions is known as group field theory (GFT). In this paper we study generalized GFT models that can be used to describe 3D quantum gravity coupled to point particles. The generalization considered is that of replacing the group leading to pure quantum gravity by the twisted product of the group with its dual-the so-called Drinfeld double of the group. The Drinfeld double is a quantum group in that it is an algebra that is both non-commutative and non-cocommutative, and special care is needed to define group field theory for it. We show how this is done, and study the resulting GFT models. Of special interest is a new topological model that is the 'Ponzano-Regge' model for the Drinfeld double. However, as we show, this model does not describe point particles. Motivated by the GFT considerations, we consider a more general class of models that are defined not using GFT, but the so-called chain mail techniques. A general model of this class does not produce 3-manifold invariants, but has an interpretation in terms of point particle Feynman diagrams

  13. Perturbative algebraic quantum field theory an introduction for mathematicians

    CERN Document Server

    Rejzner, Kasia

    2016-01-01

    Perturbative Algebraic Quantum Field Theory (pAQFT), the subject of this book, is a complete and mathematically rigorous treatment of perturbative quantum field theory (pQFT) that doesn’t require the use of divergent quantities. We discuss in detail the examples of scalar fields and gauge theories and generalize them to QFT on curved spacetimes. pQFT models describe a wide range of physical phenomena and have remarkable agreement with experimental results. Despite this success, the theory suffers from many conceptual problems. pAQFT is a good candidate to solve many, if not all of these conceptual problems. Chapters 1-3 provide some background in mathematics and physics. Chapter 4 concerns classical theory of the scalar field, which is subsequently quantized in chapters 5 and 6. Chapter 7 covers gauge theory and chapter 8 discusses QFT on curved spacetimes and effective quantum gravity. The book aims to be accessible researchers and graduate students interested in the mathematical foundations of pQFT are th...

  14. Enhancing Quantum Discord in Cavity QED by Applying Classical Driving Field

    International Nuclear Information System (INIS)

    Qian Yi; Xu Jing-Bo

    2012-01-01

    We investigate the quantum discord dynamics in a cavity quantum electrodynamics system, which consists of two noninteracting two-level atoms driven by independent optical fields and classical fields, and find that the quantum discord vanishes only asymptotically although entanglement disappears suddenly during the time evolution in the absence of classical fields. It is shown that the amount of quantum discord can be increased by adjusting the classical driving fields because the increasing degree of the amount of quantum mutual information is greater than classical correlation by applying the classical driving fields. Finally, the influence of the classical driving field on the fidelity of the system is also examined. (general)

  15. Quantum computational supremacy.

    Science.gov (United States)

    Harrow, Aram W; Montanaro, Ashley

    2017-09-13

    The field of quantum algorithms aims to find ways to speed up the solution of computational problems by using a quantum computer. A key milestone in this field will be when a universal quantum computer performs a computational task that is beyond the capability of any classical computer, an event known as quantum supremacy. This would be easier to achieve experimentally than full-scale quantum computing, but involves new theoretical challenges. Here we present the leading proposals to achieve quantum supremacy, and discuss how we can reliably compare the power of a classical computer to the power of a quantum computer.

  16. Determining Student Competency in Field Placements: An Emerging Theoretical Model

    Directory of Open Access Journals (Sweden)

    Twyla L. Salm

    2016-06-01

    Full Text Available This paper describes a qualitative case study that explores how twenty-three field advisors, representing three human service professions including education, nursing, and social work, experience the process of assessment with students who are struggling to meet minimum competencies in field placements. Five themes emerged from the analysis of qualitative interviews. The field advisors primary concern was the level of professional competency achieved by practicum students. Related to competency were themes concerned with the field advisor's role in being accountable and protecting the reputation of his/her profession as well as the reputation of the professional program affiliated with the practicum student's professional education. The final theme – teacher-student relationship –emerged from the data, both as a stand-alone and global or umbrella theme. As an umbrella theme, teacher-student relationship permeated each of the other themes as the participants interpreted their experiences of the process of assessment through the mentor relationships. A theoretical model was derived from these findings and the description of the model is presented. Cet article décrit une étude de cas qualitative qui explore comment vingt-trois conseillers de stages, représentant trois professions de services sociaux comprenant l’éducation, les soins infirmiers et le travail social, ont vécu l’expérience du processus d’évaluation avec des étudiants qui ont des difficultés à acquérir les compétences minimales durant les stages. Cinq thèmes ont été identifiés lors de l’analyse des entrevues qualitatives. La préoccupation principale des conseillers de stages était le niveau de compétence professionnelle acquis par les stagiaires. Les thèmes liés à la compétence étaient le rôle des conseillers de stages dans leur responsabilité pour protéger la réputation de leur profession ainsi que la réputation d’un programme professionnel

  17. Optical properties of an elliptic quantum ring: Eccentricity and electric field effects

    Science.gov (United States)

    Bejan, Doina; Stan, Cristina; Niculescu, Ecaterina C.

    2018-04-01

    We have theoretically studied the electronic and optical properties of a GaAs/AlGaAs elliptic quantum ring under in-plane electric field. The effects of an eccentric internal barrier -placed along the electric field direction, chosen as x-axis- and incident light polarization are particularly taken into account. The one-electron energy spectrum and wave functions are found using the adiabatic approximation and the finite element method within the effective-mass model. We show that it is possible to repair the structural distortion by applying an appropriate in-plane electric field, and the compensation is almost complete for all electronic states under study. For both concentric and eccentric quantum ring the intraband optical properties are very sensitive to the electric field and probe laser polarization. As expected, in the systems with eccentricity distortions the energy spectrum, as well as the optical response, strongly depends on the direction of the externally applied electric field, an effect that can be used as a signature of ring eccentricity. We demonstrated the possibility of generating second harmonic response at double resonance condition for incident light polarized along the x-axis if the electric field or/and eccentric barrier break the inversion symmetry. Also, strong third harmonic signal can be generated at triple resonance condition for a specific interval of electric field values when using y-polarized light.

  18. Broadband Quantum Cryptography

    CERN Document Server

    Rogers, Daniel

    2010-01-01

    Quantum cryptography is a rapidly developing field that draws from a number of disciplines, from quantum optics to information theory to electrical engineering. By combining some fundamental quantum mechanical principles of single photons with various aspects of information theory, quantum cryptography represents a fundamental shift in the basis for security from numerical complexity to the fundamental physical nature of the communications channel. As such, it promises the holy grail of data security: theoretically unbreakable encryption. Of course, implementing quantum cryptography in real br

  19. Quantum physics for beginners

    CERN Document Server

    Ficek, Zbigniew

    2016-01-01

    The textbook introduces students to the main ideas of quantum physics and the basic mathematical methods and techniques used in the fields of advanced quantum physics, atomic physics, laser physics, nanotechnology, quantum chemistry, and theoretical mathematics. The textbook explains how microscopic objects (particles) behave in unusual ways, giving rise to what's called quantum effects. It contains a wide range of tutorial problems from simple confidence-builders to fairly challenging exercises that provide adequate understanding of the basic concepts of quantum physics.

  20. Principles of physics from quantum field theory to classical mechanics

    CERN Document Server

    Jun, Ni

    2014-01-01

    This book starts from a set of common basic principles to establish the formalisms in all areas of fundamental physics, including quantum field theory, quantum mechanics, statistical mechanics, thermodynamics, general relativity, electromagnetic field, and classical mechanics. Instead of the traditional pedagogic way, the author arranges the subjects and formalisms in a logical-sequential way, i.e. all the formulas are derived from the formulas before them. The formalisms are also kept self-contained. Most of the required mathematical tools are also given in the appendices. Although this book covers all the disciplines of fundamental physics, the book is concise and can be treated as an integrated entity. This is consistent with the aphorism that simplicity is beauty, unification is beauty, and thus physics is beauty. The book may be used as an advanced textbook by graduate students. It is also suitable for physicists who wish to have an overview of fundamental physics. Readership: This is an advanced gradua...

  1. Excitations of the field-induced quantum soliton lattice in CuGeO(3).

    Science.gov (United States)

    Enderle, M; Rønnow, H M; McMorrow, D F; Regnault, L P; Dhalenne, G; Revcholevschi, A; Vorderwisch, P; Schneider, H; Smeibidl, P; Meissner, M

    2001-10-22

    The incommensurate magnetic soliton lattice in the high-field phase of a spin-Peierls system results from quantum fluctuations. We have used neutron scattering techniques to study CuGeO(3), allowing us to obtain the first complete characterization of the excitations of the soliton lattice. Three distinct excitation branches are observed, all of which are gapped. The two highest energy modes have minimum gaps at the commensurate wave vector and correspond to the creation or annihilation of soliton pairs. The third mode is incommensurate and is discussed in relation to theoretical predictions.

  2. Regularization of the quantum field theory of charges and monopoles

    International Nuclear Information System (INIS)

    Panagiotakopoulos, C.

    1981-09-01

    A gauge invariant regularization procedure for quantum field theories of electric and magnetic charges based on Zwanziger's local formulation is proposed. The bare regularized full Green's functions of gauge invariant operators are shown to be Lorentz invariant. This would have as a consequence the Lorentz invariance of the finite Green's functions that might result after any reasonable subtraction if such a subtraction can be found. (author)

  3. Anisotropy of exciton spectrum and spin-orbit interactions in quantum wells in tilted magnetic field

    International Nuclear Information System (INIS)

    Olendski, Oleg; Shahbazyan, Tigran V

    2006-01-01

    We study theoretically excitonic energy spectrum and optical absorption in narrowgap semiconductor quantum wells in strong magnetic field. We show that, in the presence of an in-plane field component, the absorption coefficient exhibit a double-peak structure due to hybridization of bright and dark excitons. If both Rashba and Dresselhaus spin-orbit terms are present, the spectrum is anisotropic in in-plane field orientation with respect to [100] axis. In particular, the magnitude of the splitting can be tuned in a wide interval by varying the azimuthal angle of the in-plane field. The absorption spectrrum anisotropy would allow simultaneous measurement Dresselhaus and Rashba spin-orbit coefficients

  4. Quantum mechanics. Mechanically detecting and avoiding the quantum fluctuations of a microwave field.

    Science.gov (United States)

    Suh, J; Weinstein, A J; Lei, C U; Wollman, E E; Steinke, S K; Meystre, P; Clerk, A A; Schwab, K C

    2014-06-13

    Quantum fluctuations of the light field used for continuous position detection produce stochastic back-action forces and ultimately limit the sensitivity. To overcome this limit, the back-action forces can be avoided by giving up complete knowledge of the motion, and these types of measurements are called "back-action evading" or "quantum nondemolition" detection. We present continuous two-tone back-action evading measurements with a superconducting electromechanical device, realizing three long-standing goals: detection of back-action forces due to the quantum noise of a microwave field, reduction of this quantum back-action noise by 8.5 ± 0.4 decibels (dB), and measurement imprecision of a single quadrature of motion 2.4 ± 0.7 dB below the mechanical zero-point fluctuations. Measurements of this type will find utility in ultrasensitive measurements of weak forces and nonclassical states of motion. Copyright © 2014, American Association for the Advancement of Science.

  5. Classical and quantum chaos in a quantum dot in time-periodic magnetic fields

    Science.gov (United States)

    Badrinarayanan, R.; José, Jorge V.

    1996-09-01

    We investigate the classical and quantum dynamics of an electron confined to a circular quantum dot in the presence of homogeneous Bdc+Bac magnetic fields. The classical motion shows a transition to chaotic behavior depending on the ratio ɛ=Bac/Bdc of field magnitudes and the cyclotron frequency ω~c in units of the drive frequency. We determine a phase boundary between regular and chaotic classical behavior in the ɛ vs ω~c plane. In the quantum regime we evaluate the quasienergy spectrum of the time-evolution operator. We show that the nearest-neighbor quasienergy eigenvalues show a transition from level clustering to level repulsion as one moves from the regular to chaotic regime in the (ɛ,ω~c) plane. The Δ3 statistic confirms this transition. In the chaotic regime, the eigenfunction statistics coincides with the Porter-Thomas prediction. Finally, we explicitly establish the phase-space correspondence between the classical and quantum solutions via the Husimi phase-space distributions of the model. Possible experimentally feasible conditions to see these effects are discussed.

  6. Charge-field formulation of quantum electrodynamics (QEMED)

    International Nuclear Information System (INIS)

    Leiter, D.

    1980-01-01

    By expressing classical electron theory in terms of 'charge-field' functional structures, it is shown that a finite formulation of the classical electrodynamics of point charges emerges in a simple and elegant fashion. This is used to construct a 'charge-field' quantum electrodynamic theory. It is found that interacting photon states are generated as a secondary manifestation of electron-positron quantization, and do not require the usual 'free' canonical quantization scheme. The possibility is discussed that this approach may lead to a better formulation of quantum electrodynamics in the Heisenberg picture and suggests a crucial experimental test to distinguish this new 'charge-field' quantum electrodynamics 'QEMED' from the standard QED formulation. Specifically QEMED predicts that the 'Einstein principle of separability' should be found to be valid for correlated photon polarization measurements, in which the polarizers are changed more rapidly than a characteristic photon travel time. Such an experiment (Aspect 1976) can distinguish between QEMED and QED in a complete and clear-cut fashion. (U.K.)

  7. A new formulation of quantum field theory on S4

    International Nuclear Information System (INIS)

    Harris, B.A.; Joshi, G.C.

    1993-01-01

    Recent developments in quantum gravity suggest that wormholes may influence the observed values of the constants of nature. The Euclidean formulation of quantum gravity predicts that wormholes induce a probability distribution in the space of possible fundamentals constants. In particular, the effective action on a large spherical space may lead to the vanishing of the cosmological constant and possibly determine the values of other constants of nature. The ability to perform calculations involving interacting quantum fields, particularly non-Abelian models, on a four-sphere is vital if one is to investigate this possibility. In this paper, a new formulation of field theory on a four-sphere is presented using the angular momentum space representation of SO(5). A review of field theory on a sphere is given and then show how a matrix element prescription in angular momentum space and a new summation technique based on the complex l-plane, overcome previous limitations in calculation techniques. The standard one-loop graphs of QED are given as examples. 13 refs., 3 figs

  8. Nonequilibrium forces between neutral atoms mediated by a quantum field

    International Nuclear Information System (INIS)

    Behunin, Ryan O.; Hu, Bei-Lok

    2010-01-01

    We study forces between two neutral atoms, modeled as three-dimensional harmonic oscillators, arising from mutual influences mediated by an electromagnetic field but not from their direct interactions. We allow as dynamical variables the center-of-mass motion of the atom, its internal degrees of freedom, and the quantum field treated relativistically. We adopt the method of nonequilibrium quantum field theory which can provide a first-principles, systematic, and unified description including the intrinsic and induced dipole fluctuations. The inclusion of self-consistent back-actions makes possible a fully dynamical description of these forces valid for general atom motion. In thermal equilibrium we recover the known forces--London, van der Waals, and Casimir-Polder--between neutral atoms in the long-time limit. We also reproduce a recently reported force between atoms when the system is out of thermal equilibrium at late times. More noteworthy is the discovery of the existence of a type of (or identification of the source of some known) interatomic force which we call the ''entanglement force,'' originating from the quantum correlations of the internal degrees of freedom of entangled atoms.

  9. Particle versus field structure in conformal quantum field theories

    International Nuclear Information System (INIS)

    Schroer, Bert

    2000-06-01

    I show that a particle structure in conformal field theory is incompatible with interactions. As a substitute one has particle-like excitations whose interpolating fields have in addition to their canonical dimension an anomalous contribution. The spectra of anomalous dimension is given in terms of the Lorentz invariant quadratic invariant (compact mass operator) of a conformal generator R μ with pure discrete spectrum. The perturbative reading of R o as a Hamiltonian in its own right, associated with an action in a functional integral setting naturally leads to the Ad S formulation. The formal service role of Ad S in order to access C QFT by a standard perturbative formalism (without being forced to understand first massive theories and then taking their scale-invariant limit) vastly increases the realm of conventionally accessible 4-dim. C QFT beyond those for which one had to use Lagrangians with supersymmetry in order to have a vanishing Beta-function. (author)

  10. “Hot entanglement”? – A nonequilibrium quantum field theory scrutiny

    Energy Technology Data Exchange (ETDEWEB)

    Hsiang, J.-T., E-mail: cosmology@gmail.com [Center for Particle Physics and Field Theory, Department of Physics, Fudan University, Shanghai 200433 (China); Hu, B.L., E-mail: blhu@umd.edu [Center for Particle Physics and Field Theory, Department of Physics, Fudan University, Shanghai 200433 (China); Maryland Center for Fundamental Physics and Joint Quantum Institute, University of Maryland, College Park, MD 20742 (United States)

    2015-11-12

    The possibility of maintaining entanglement in a quantum system at finite, even high, temperatures – the so-called ‘hot entanglement’ – has obvious practical interest, but also requires closer theoretical scrutiny. Since quantum entanglement in a system evolves in time and is continuously subjected to environmental degradation, a nonequilibrium description by way of open quantum systems is called for. To identify the key issues and the contributing factors that may permit ‘hot entanglement’ to exist, or the lack thereof, we carry out a model study of two spatially-separated, coupled oscillators in a shared bath depicted by a finite-temperature scalar field. From the Langevin equations we derived for the normal modes and the entanglement measure constructed from the covariance matrix we examine the interplay between direct coupling, field-induced interaction and finite separation on the structure of late-time entanglement. We show that the coupling between oscillators plays a crucial role in sustaining entanglement at intermediate temperatures and over finite separations. In contrast, the field-induced interaction between the oscillators which is a non-Markovian effect becomes very ineffective at high temperature. We determine the critical temperature above which entanglement disappears to be bounded in the leading order by the inverse frequency of the center-of-mass mode of the reduced oscillator system, a result not unexpected, which rules out hot entanglement in such settings.

  11. “Hot entanglement”? – A nonequilibrium quantum field theory scrutiny

    Directory of Open Access Journals (Sweden)

    J.-T. Hsiang

    2015-11-01

    Full Text Available The possibility of maintaining entanglement in a quantum system at finite, even high, temperatures – the so-called ‘hot entanglement’ – has obvious practical interest, but also requires closer theoretical scrutiny. Since quantum entanglement in a system evolves in time and is continuously subjected to environmental degradation, a nonequilibrium description by way of open quantum systems is called for. To identify the key issues and the contributing factors that may permit ‘hot entanglement’ to exist, or the lack thereof, we carry out a model study of two spatially-separated, coupled oscillators in a shared bath depicted by a finite-temperature scalar field. From the Langevin equations we derived for the normal modes and the entanglement measure constructed from the covariance matrix we examine the interplay between direct coupling, field-induced interaction and finite separation on the structure of late-time entanglement. We show that the coupling between oscillators plays a crucial role in sustaining entanglement at intermediate temperatures and over finite separations. In contrast, the field-induced interaction between the oscillators which is a non-Markovian effect becomes very ineffective at high temperature. We determine the critical temperature above which entanglement disappears to be bounded in the leading order by the inverse frequency of the center-of-mass mode of the reduced oscillator system, a result not unexpected, which rules out hot entanglement in such settings.

  12. Calculation of Zeeman splitting and Zeeman transition energies of spherical quantum dot in uniform magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Çakır, Bekir; Atav, Ülfet [Physics Department, Faculty of Sciences, Selcuk University, Campus 42031 Konya (Turkey); Yakar, Yusuf, E-mail: yuyakar@yahoo.com [Physics Department, Faculty of Arts and Sciences, Aksaray University, Campus 68100 Aksaray (Turkey); Özmen, Ayhan [Physics Department, Faculty of Sciences, Selcuk University, Campus 42031 Konya (Turkey)

    2016-08-22

    Highlights: • The magnetic field effects on the ground and excited energy states of QD are investigated. • The Zeeman transition energies between energy states are calculated. • Wave functions and the energy eigenvalues are computed by using Quantum Genetic Algorithm and Hartree–Fock Roothaan method. - Abstract: In this study we report a detailed theoretical investigation of the effect of an external magnetic field on the 1s-, 2p-, 3d- and 4f-energy states of a spherical quantum dot. We treat the contribution of the diamagnetic term as a perturbation and discuss the effect of the diamagnetic term on the 1s-, 2p-, 3d- and 4f-energy states. We also have calculated the Zeeman transition energies between 2p → 1s and 3d → 2p states with m = 0, ±1 and 0, ±1, ±2 as a function of dot radius and the magnetic field strength. The results show that the magnetic field, impurity charge and dot radius have a strong influence on the energy states and the Zeeman transitions. It is found that the energies of the electronic states with m < 0 addition of the diamagnetic term firstly decrease toward a minimum, and then increase with the increasing magnetic field strength. We have seen that as magnetic field intensity is adjusted, frequency of the emitted light can be changed for Zeeman transitions.

  13. Complexity in quantum field theory and physics beyond the standard model

    International Nuclear Information System (INIS)

    Goldfain, Ervin

    2006-01-01

    Complex quantum field theory (abbreviated c-QFT) is introduced in this paper as an alternative framework for the description of physics beyond the energy range of the standard model. The mathematics of c-QFT is based on fractal differential operators that generalize the momentum operators of conventional quantum field theory (QFT). The underlying premise of our approach is that c-QFT contains the right analytical tools for dealing with the asymptotic regime of QFT. Canonical quantization of c-QFT leads to the following findings: (i) the Fock space of c-QFT includes fractional numbers of particles and antiparticles per state (ii) c-QFT represents a generalization of topological field theory and (iii) classical limit of c-QFT is equivalent to field theory in curved space-time. The first finding provides a field-theoretic motivation for the transfinite discretization approach of El-Naschie's ε (∞) theory. The second and third findings suggest the dynamic unification of boson and fermion fields as particles with fractional spin, as well as the close connection between spin and space-time topology beyond the conventional physics of the standard model

  14. Quantum physics meets the philosophy of mind new essays on the mind-body relation in quantum-theoretical perspective

    CERN Document Server

    Meixner, Uwe

    2014-01-01

    Quantum physics, unlike classical physics, suggests a non-physicalistic metaphysics. Whereas physicalism implies a reductive position in the philosophy of mind, quantum physics is compatible with non-reductionism, and actually seems to support it. The essays in this book explore, from various points of view, the possibilities of basing a non-reductive philosophy of mind on quantum physics.

  15. Relativistic many-body theory a new field-theoretical approach

    CERN Document Server

    Lindgren, Ingvar

    2016-01-01

    This revised second edition of the author’s classic text offers readers a comprehensively updated review of relativistic atomic many-body theory, covering the many developments in the field since the publication of the original title.  In particular, a new final section extends the scope to cover the evaluation of QED effects for dynamical processes. The treatment of the book is based upon quantum-field theory, and demonstrates that when the procedure is carried to all orders of perturbation theory, two-particle systems are fully compatible with the relativistically covariant Bethe-Salpeter equation. This procedure can be applied to arbitrary open-shell systems, in analogy with the standard many-body theory, and it is also applicable to systems with more than two particles. Presently existing theoretical procedures for treating atomic systems are, in several cases, insufficient to explain the accurate experimental data recently obtained, particularly for highly charged ions. The main text is divided into...

  16. Perturbative Field-Theoretical Renormalization Group Approach to Driven-Dissipative Bose-Einstein Criticality

    Directory of Open Access Journals (Sweden)

    Uwe C. Täuber

    2014-04-01

    Full Text Available The universal critical behavior of the driven-dissipative nonequilibrium Bose-Einstein condensation transition is investigated employing the field-theoretical renormalization group method. Such criticality may be realized in broad ranges of driven open systems on the interface of quantum optics and many-body physics, from exciton-polariton condensates to cold atomic gases. The starting point is a noisy and dissipative Gross-Pitaevski equation corresponding to a complex-valued Landau-Ginzburg functional, which captures the near critical nonequilibrium dynamics, and generalizes model A for classical relaxational dynamics with nonconserved order parameter. We confirm and further develop the physical picture previously established by means of a functional renormalization group study of this system. Complementing this earlier numerical analysis, we analytically compute the static and dynamical critical exponents at the condensation transition to lowest nontrivial order in the dimensional ε expansion about the upper critical dimension d_{c}=4 and establish the emergence of a novel universal scaling exponent associated with the nonequilibrium drive. We also discuss the corresponding situation for a conserved order parameter field, i.e., (subdiffusive model B with complex coefficients.

  17. Quantum theory of strong-field frustrated tunneling

    Science.gov (United States)

    Popruzhenko, S. V.

    2018-01-01

    We show how the strong-field approximation, widely used for description of multiphoton and tunneling ionization, can be extended to analyse the excitation of bound states in intense low-frequency laser pulses. The proposed theory is based on the formalism of quantum trajectories and fills the gap between the numerical solution of the time-dependent Schrödinger equation and classical simulations. In particular, it allows identifying non-adiabatic and interference effects in strong-field excitation of Rydberg states.

  18. Quantum processes in a strong electromagnetic field producing pairs. 3

    International Nuclear Information System (INIS)

    Gitman, D.M.; Gavrilov, S.P.

    1977-01-01

    The Furry picture in quantum electrodynamics with an external field producing real pairs has been generalized. For the required generalization to be achieved all operators of a spinor field are expressed through functions of production and annihilation operators and formulated are the rules for reduction to a generalized normal form, i.e., to such a form in which all the production operators in each term are on the left from all the annihilation operators. The diagram technique for matrix elements of random processes has been considered

  19. A course on quantum field theory and local observables

    Energy Technology Data Exchange (ETDEWEB)

    Schroer, Bert [Frankfurt Univ., Berlin (Germany). Inst. fuer Theoretische Physik

    1997-03-01

    A monograph on Quantum Field Theory and Local Observables is presented, aiming to unify two presently largely disconnected branches of QFT, as follows: the standard (canonical, functional) approach which is mainly perturbative in the sense of an infinitesimal `deformation` of free fields; nonperturbative constructions of low-dimensional models as the form factor-bootstrap approach (which for the time being is limited to factorable models in d=1+1 spacetime dimensions) and the non-Lagrangian constructions of conformal chiral QFT`s

  20. Field dependence of the electron spin relaxation in quantum dots.

    Science.gov (United States)

    Calero, Carlos; Chudnovsky, E M; Garanin, D A

    2005-10-14

    The interaction of the electron spin with local elastic twists due to transverse phonons is studied. The universal dependence of the spin-relaxation rate on the strength and direction of the magnetic field is obtained in terms of the electron gyromagnetic tensor and macroscopic elastic constants of the solid. The theory contains no unknown parameters and it can be easily tested in experiment. At high magnetic field it provides a parameter-free lower bound on the electron spin relaxation in quantum dots.

  1. Fluctuations of quantum fields via zeta function regularization

    International Nuclear Information System (INIS)

    Cognola, Guido; Zerbini, Sergio; Elizalde, Emilio

    2002-01-01

    Explicit expressions for the expectation values and the variances of some observables, which are bilinear quantities in the quantum fields on a D-dimensional manifold, are derived making use of zeta function regularization. It is found that the variance, related to the second functional variation of the effective action, requires a further regularization and that the relative regularized variance turns out to be 2/N, where N is the number of the fields, thus being independent of the dimension D. Some illustrating examples are worked through. The issue of the stress tensor is also briefly addressed

  2. A theoretical quantum chemical study of alanine formation in interstellar medium

    Science.gov (United States)

    Shivani; Pandey, Parmanad; Misra, Alka; Tandon, Poonam

    2017-08-01

    The interstellar medium, the vast space between the stars, is a rich reservoir of molecular material ranging from simple diatomic molecules to more complex, astrobiologically important molecules such as amino acids, nucleobases, and other organic species. Radical-radical and radical-neutral interaction schemes are very important for the formation of comparatively complex molecules in low temperature chemistry. An attempt has been made to explore the possibility of formation of complex organic molecules in interstellar medium, through detected interstellar molecules like CH3CN and HCOOH. The gas phase reactions are theoretically studied using quantum chemical techniques. We used the density functional theory (DFT) at the B3LYP/6-311G( d, p) level. The reaction energies, potential barrier and optimized structures of all the geometries, involved in the reaction path, has been discussed. We report the potential energy surfaces for the reactions considered in this work.

  3. Quantum Humor: The Playful Side of Physics at Bohr's Institute for Theoretical Physics

    Science.gov (United States)

    Halpern, Paul

    2012-09-01

    From the 1930s to the 1950s, a period of pivotal developments in quantum, nuclear, and particle physics, physicists at Niels Bohr's Institute for Theoretical Physics in Copenhagen took time off from their research to write humorous articles, letters, and other works. Best known is the Blegdamsvej Faust, performed in April 1932 at the close of one of the Institute's annual conferences. I also focus on the Journal of Jocular Physics, a humorous tribute to Bohr published on the occasions of his 50th, 60th, and 70th birthdays in 1935, 1945, and 1955. Contributors included Léon Rosenfeld, Victor Weisskopf, George Gamow, Oskar Klein, and Hendrik Casimir. I examine their contributions along with letters and other writings to show that they offer a window into some issues in physics at the time, such as the interpretation of complementarity and the nature of the neutrino, as well as the politics of the period.

  4. Information-theoretic security proof for quantum-key-distribution protocols

    International Nuclear Information System (INIS)

    Renner, Renato; Gisin, Nicolas; Kraus, Barbara

    2005-01-01

    We present a technique for proving the security of quantum-key-distribution (QKD) protocols. It is based on direct information-theoretic arguments and thus also applies if no equivalent entanglement purification scheme can be found. Using this technique, we investigate a general class of QKD protocols with one-way classical post-processing. We show that, in order to analyze the full security of these protocols, it suffices to consider collective attacks. Indeed, we give new lower and upper bounds on the secret-key rate which only involve entropies of two-qubit density operators and which are thus easy to compute. As an illustration of our results, we analyze the Bennett-Brassard 1984, the six-state, and the Bennett 1992 protocols with one-way error correction and privacy amplification. Surprisingly, the performance of these protocols is increased if one of the parties adds noise to the measurement data before the error correction. In particular, this additional noise makes the protocols more robust against noise in the quantum channel

  5. Information-theoretic security proof for quantum-key-distribution protocols

    Science.gov (United States)

    Renner, Renato; Gisin, Nicolas; Kraus, Barbara

    2005-07-01

    We present a technique for proving the security of quantum-key-distribution (QKD) protocols. It is based on direct information-theoretic arguments and thus also applies if no equivalent entanglement purification scheme can be found. Using this technique, we investigate a general class of QKD protocols with one-way classical post-processing. We show that, in order to analyze the full security of these protocols, it suffices to consider collective attacks. Indeed, we give new lower and upper bounds on the secret-key rate which only involve entropies of two-qubit density operators and which are thus easy to compute. As an illustration of our results, we analyze the Bennett-Brassard 1984, the six-state, and the Bennett 1992 protocols with one-way error correction and privacy amplification. Surprisingly, the performance of these protocols is increased if one of the parties adds noise to the measurement data before the error correction. In particular, this additional noise makes the protocols more robust against noise in the quantum channel.

  6. Quantum mechanics and the particles of nature. An outline for mathematicians

    Energy Technology Data Exchange (ETDEWEB)

    Sudbery, Anthony

    1986-01-01

    The book gives the basic theoretical concepts of quantum mechanics and particle physics, and is aimed at the final year undergraduates in mathematics or physics. The contents contain seven chapters on:-particles and forces, quantum statics, quantum dynamics, quantum systems, quantum metaphysics, quantum numbers and quantum fields.

  7. Electron-electron interactions in graphene field-induced quantum dots in a high magnetic field

    DEFF Research Database (Denmark)

    Orlof, A.; Shylau, Artsem; Zozoulenko, I. V.

    2015-01-01

    We study the effect of electron-electron interaction in graphene quantum dots defined by an external electrostatic potential and a high magnetic field. To account for the electron-electron interaction, we use the Thomas-Fermi approximation and find that electron screening causes the formation...... of compressible strips in the potential profile and the electron density. We numerically solve the Dirac equations describing the electron dynamics in quantum dots, and we demonstrate that compressible strips lead to the appearance of plateaus in the electron energies as a function of the magnetic field. Finally...

  8. Quantum control mechanism analysis through field based Hamiltonian encoding

    International Nuclear Information System (INIS)

    Mitra, Abhra; Rabitz, Herschel

    2006-01-01

    Optimal control of quantum dynamics in the laboratory is proving to be increasingly successful. The control fields can be complex, and the mechanisms by which they operate have often remained obscure. Hamiltonian encoding (HE) has been proposed as a method for understanding mechanisms in quantum dynamics. In this context mechanism is defined in terms of the dominant quantum pathways leading to the final state of the controlled system. HE operates by encoding a special modulation into the Hamiltonian and decoding its signature in the dynamics to determine the dominant pathway amplitudes. Earlier work encoded the modulation directly into the Hamiltonian operators. This present work introduces the alternative scheme of field based HE, where the modulation is encoded into the control field and not directly into the Hamiltonian operators. This distinct form of modulation yields a new perspective on mechanism and is computationally faster than the earlier approach. Field based encoding is also an important step towards a laboratory based algorithm for HE as it is the only form of encoding that may be experimentally executed. HE is also extended to cover systems with noise and uncertainty and finally, a hierarchical algorithm is introduced to reveal mechanism in a stepwise fashion of ever increasing detail as desired. This new hierarchical algorithm is an improvement over earlier approaches to HE where the entire mechanism was determined in one stroke. The improvement comes from the use of less complex modulation schemes, which leads to fewer evaluations of Schroedinger's equation. A number of simulations are presented on simple systems to illustrate the new field based encoding technique for mechanism assessment

  9. Quantum mean-field theory of collective dynamics and tunneling

    Energy Technology Data Exchange (ETDEWEB)

    Negele, J.W.

    1981-01-01

    A fundamental problem in quantum many-body theory is formulation of a microscopic theory of collective motion. For self-bound, saturating systems like finite nuclei described in the context of nonrelativistic quantum mechanics with static interactions, the essential problem is how to formulate a systematic quantal theory in which the relevant collective variables and their dynamics arise directly and naturally from the Hamiltonian and the system under consideration. Significant progress has been made recently in formulating the quantum many-body problem in terms of an expansion about solutions to time-dependent mean-field equations. The essential ideas, principal results, and illustrative examples are summarized. An exact expression for an observable of interest is written using a functional integral representation for the evolution operator, and tractable time-dependent mean field equations are obtained by application of the stationary-phase approximation (SPA) to the functional integral. Corrections to the lowest-order theory may be systematically enumerated. 6 figures. (RWR)

  10. The Quantum Space Phase Transitions for Particles and Force Fields

    Directory of Open Access Journals (Sweden)

    Chung D.-Y.

    2006-07-01

    Full Text Available We introduce a phenomenological formalism in which the space structure is treated in terms of attachment space and detachment space. Attachment space attaches to an object, while detachment space detaches from the object. The combination of these spaces results in three quantum space phases: binary partition space, miscible space and binary lattice space. Binary lattice space consists of repetitive units of alternative attachment space and detachment space. In miscible space, attachment space is miscible to detachment space, and there is no separation between attachment space and detachment spaces. In binary partition space, detachment space and attachment space are in two separat continuous regions. The transition from wavefunction to the collapse of wavefuction under interference becomes the quantum space phase transition from binary lattice space to miscible space. At extremely conditions, the gauge boson force field undergoes a quantum space phase transition to a "hedge boson force field", consisting of a "vacuum" core surrounded by a hedge boson shell, like a bubble with boundary.

  11. Mathematica for Theoretical Physics: Electrodynamics, Quantum Mechanics, General Relativity and Fractals

    Energy Technology Data Exchange (ETDEWEB)

    Heusler, Stefan [Duisburg-Essen University, 47057 Duisburg (Germany)

    2006-12-08

    The main focus of the second, enlarged edition of the book Mathematica for Theoretical Physics is on computational examples using the computer program Mathematica in various areas in physics. It is a notebook rather than a textbook. Indeed, the book is just a printout of the Mathematica notebooks included on the CD. The second edition is divided into two volumes, the first covering classical mechanics and nonlinear dynamics, the second dealing with examples in electrodynamics, quantum mechanics, general relativity and fractal geometry. The second volume is not suited for newcomers because basic and simple physical ideas which lead to complex formulas are not explained in detail. Instead, the computer technology makes it possible to write down and manipulate formulas of practically any length. For researchers with experience in computing, the book contains a lot of interesting and non-trivial examples. Most of the examples discussed are standard textbook problems, but the power of Mathematica opens the path to more sophisticated solutions. For example, the exact solution for the perihelion shift of Mercury within general relativity is worked out in detail using elliptic functions. The virial equation of state for molecules' interaction with Lennard-Jones-like potentials is discussed, including both classical and quantum corrections to the second virial coefficient. Interestingly, closed solutions become available using sophisticated computing methods within Mathematica. In my opinion, the textbook should not show formulas in detail which cover three or more pages-these technical data should just be contained on the CD. Instead, the textbook should focus on more detailed explanation of the physical concepts behind the technicalities. The discussion of the virial equation would benefit much from replacing 15 pages of Mathematica output with 15 pages of further explanation and motivation. In this combination, the power of computing merged with physical intuition

  12. Symmetry breaking due to quantum fluctuations in massless field theories

    International Nuclear Information System (INIS)

    Ghose, P.; Datta, A.

    1977-10-01

    It is shown that quantum fluctuations can act as the driving mechanism for the spontaneous breakdown of both scale and the discrete phi→-phi symmetries in a lamdaphi 4 theory which is massless and scale invariant in the tree approximation. Consequently dimensional transformation occurs and the dimensionless and only parameter lambda in the theory is fixed and replaced by the vacuum expectation value of the field. These results are shown to be consistent with the appropriate renormalization group equation for the theory. A scalar electrodynamics which is massless and scale invariant in the tree approximation is also considered, and it is shown that the Higgs meson in such a theory is much heavier than the vector meson for small values of the gauge coupling constant e. Another interesting consequence of such a theory is that it possesses vortex-line solutions only when quantum fluctuations are taken into account

  13. Scaling algebras and renormalization group in algebraic quantum field theory

    International Nuclear Information System (INIS)

    Buchholz, D.; Verch, R.

    1995-01-01

    For any given algebra of local observables in Minkowski space an associated scaling algebra is constructed on which renormalization group (scaling) transformations act in a canonical manner. The method can be carried over to arbitrary spacetime manifolds and provides a framework for the systematic analysis of the short distance properties of local quantum field theories. It is shown that every theory has a (possibly non-unique) scaling limit which can be classified according to its classical or quantum nature. Dilation invariant theories are stable under the action of the renormalization group. Within this framework the problem of wedge (Bisognano-Wichmann) duality in the scaling limit is discussed and some of its physical implications are outlined. (orig.)

  14. Introduction to a field-theoretical treatment of neutrino oscillations

    Indian Academy of Sciences (India)

    Keywords. Neutrino mass; laboratory experiments on neutrino mass; field theory ... of the neutrino mass eigenfields. We show that this field-theoretical approach leads to a transparent treatment of neutrino oscillations without ambiguities and provides the correct answer in cases where the standard approach fails.

  15. Field-theoretic calculation of kinetic helicity flux

    Indian Academy of Sciences (India)

    Given all these practical aspects, kinetic helicity is an important quantity to study in fluid turbulence. Turbulence involves millions of interacting modes. It is very difficult to analyze these modes theoretically as well as numerically. In recent times, a new numeri- cal procedure called 'large eddy simulations' (LES) has become ...

  16. Hybridization of electron states in a step quantum well in a magnetic field

    International Nuclear Information System (INIS)

    Barseghyan, M.G.; Kirakosyan, A.A.

    2005-01-01

    The quantum states and energy levels of an electrion in a rectangular step quantum well in a magnetic field parallel to the plane of two-dimentional electron gas are investigated. It is shown that the joint effect of the magnetic field and confining potential of the quantum well results in redical change of the electron spectrum. The dependence of the electron energy levels on the quantum well parameters, magnetic field induction and projection of the wave-vector along the magnetic field induction are calculated. Numerical calculations are carried out for a AlAs/GaAlAs/GaAs/AlAs step quantum well

  17. Effects of electric field and light polarization on the electromagnetically induced transparency in an impurity doped quantum ring

    Science.gov (United States)

    Bejan, D.; Stan, C.; Niculescu, E. C.

    2018-01-01

    We theoretically investigated the effects of the impurity position, in-plane electric field, intensity and polarization of the probe and control lasers on the electromagnetically induced transparency (EIT) in GaAs/GaAlAs disc shaped quantum ring. Our study reveals that, depending on the impurity position, the quantum system presents two specific configurations for the EIT occurrence even in the absence of the external electric field, i.e. ladder-configuration or V-configuration, and changes the configuration from ladder to V for specific electric field values. The polarization of the probe and control lasers plays a crucial role in obtaining a good transparency. The electric field controls the red-shift (blue-shift) of the transparency window and modifies its width. The system exhibits birefringence for the probe light in a limited interval of electric field values.

  18. Quantum capacitance of an ultrathin topological insulator film in a magnetic field

    KAUST Repository

    Tahir, M.

    2013-02-12

    We present a theoretical study of the quantum magnetocapacitance of an ultrathin topological insulator film in an external magnetic field. The study is undertaken to investigate the interplay of the Zeeman interaction with the hybridization between the upper and lower surfaces of the thin film. Determining the density of states, we find that the electron-hole symmetry is broken when the Zeeman and hybridization energies are varied relative to each other. This leads to a change in the character of the magnetocapacitance at the charge neutrality point. We further show that in the presence of both Zeeman interaction and hybridization the magnetocapacitance exhibits beating at low and splitting of the Shubnikov de Haas oscillations at high perpendicular magnetic field. In addition, we address the crossover from perpendicular to parallel magnetic field and find consistency with recent experimental data.

  19. Operator product expansions on the vacuum in conformal quantum field theory in two spacetime dimensions

    International Nuclear Information System (INIS)

    Luescher, M.

    1975-11-01

    Let phi 1 (x) and phi 2 (y) be two local fields in a conformal quantum field theory (CQFT) in two-dimensional spacetime. It is then shown that the vector-valued distribution phi 1 (x) phi 2 (y) /0 > is a boundary value of a vector-valued holomorphic function which is defined on a large conformally invariant domain. By group theoretical arguments alone it is proved that phi 1 (x) phi 2 (y) /0 > can be expanded into conformal partial waves. These have all the properties of a global version of Wilson's operator product expansions when applied to the vacuum state /0 >. Finally, the corresponding calculations are carried out more explicitly in the Thirring model. Here, a complete set of local conformally covariant fields is found, which is closed under vacuum expansion of any two of its elements (a vacuum expansion is an operator product expansion applied to the vacuum). (orig.) [de

  20. Quantum field theory in curved space-time

    International Nuclear Information System (INIS)

    Najmi, A.-H.

    1982-09-01

    The problem of constructing states for quantum field theories in nonstationary background space-times is set out. A formalism in which the problem of constructing states can be attacked more easily than at present is presented. The ansatz of energy-minimization as a means of constructing states is formulated in this formalism and its general solution for the free scalar field is found. It has been known, in specific cases, that such states suffer from the problem of unitary inequivalence (the pathology). An example in Minowski space-time is presented in which global operators, such as the particle-number operator, do not exist but all physical observables, such as the renormalized energy density are finite. This model has two Fock-sectors as its space of physical states. A simple extension of this model, i.e. enlarging the Fock-space of states is found not to remedy the pathology: in a Robertson-Walker space-time the quantum field acquires an infinite amount of renormalized energy density to the future of the hypersurface on which the energy density is minimized. Finally, the solution of the ansatz of energy minimization for the free, massive Hermitian fermion field is presented. (author)

  1. Quantum double actions on operator algebras and orbifold quantum field theories

    International Nuclear Information System (INIS)

    Mueger, M.

    1996-06-01

    Starting from a local quantum field theory with an unbroken compact symmetry group G in 1+1 dimensional spacetime we construct disorder fields implementing gauge transformations on the fields (order variables) localized in a wedge region. Enlarging the local algebras by these disorder fields we obtain a nonlocal field theory, the fixpoint algebras of which under the appropriately extended action of the group G are shown to satisfy Haag duality in every simple sector. The specifically 1+1 dimensional phenomenon of violation of Haag duality of fixpoint nets is thereby clarified. In the case of a finite group G the extended theory is acted upon in a completely canonical way by the quantum double D(G) and satisfies R-matrix commutation relations as well as a Verlinde algebra. Furthermore, our methods are suitable for a concise and transparent approach to bosonization. The main technical ingredient is a strengthened version of the split property which should hold in all reasonable massive theories. In the appendices (part of) the results are extended to arbitary locally compact groups and our methods are adapted to chiral theories on the circle. (orig.)

  2. Quantum systems with finite Hilbert space: Galois fields in quantum mechanics

    International Nuclear Information System (INIS)

    Vourdas, A

    2007-01-01

    A 'Galois quantum system' in which the position and momentum take values in the Galois field GF(p l ) is considered. It is comprised of l-component systems which are coupled in a particular way and is described by a certain class of Hamiltonians. Displacements in the GF(p l ) x GF(p l ) phase space and the corresponding Heisenberg-Weyl group are studied. Symplectic transformations are shown to form the Sp(2, GF(p l )) group. Wigner and Weyl functions are defined and their properties are studied. Frobenius symmetries, which are based on Frobenius automorphisms in the theory of Galois fields, are a unique feature of these systems (for l ≥ 2). If they commute with the Hamiltonian, there are constants of motion which are discussed. An analytic representation in the l-sheeted complex plane provides an elegant formalism that embodies the properties of Frobenius transformations. The difference between a Galois quantum system and other finite quantum systems where the position and momentum take values in the ring [Z p l ] is discussed. (topical review)

  3. Reentrant quantum anomalous Hall effect with in-plane magnetic fields in HgMnTe quantum wells

    Science.gov (United States)

    Hsu, Hsiu-Chuan; Liu, Xin; Liu, Chao-Xing

    2013-08-01

    The quantum anomalous Hall effect has been predicted in HgMnTe quantum wells with an out-of-plane magnetization of Mn atoms. However, since HgMnTe quantum wells are paramagnetic, an out-of-plane magnetic field is required to polarize magnetic moments of Mn atoms, which inevitably induces Landau levels and makes it difficult to identify the origin of the quantized Hall conductance experimentally. In this work, we study the quantum anomalous Hall effect in the presence of an in-plane magnetic field in Mn-doped HgTe quantum wells. For a small out-of-plane magnetic field, the in-plane magnetic field can drive the system from a normal insulating state to a quantum anomalous Hall state. When the out-of-plane magnetic field is slightly above the transition point, the system shows a reentrant behavior of Hall conductance, varying from -e2/h to 0 and back to -e2/h, with increasing in-plane magnetic fields. The reentrant quantum anomalous Hall effect originates from the interplay between the exchange coupling of magnetic moments and the direct Zeeman coupling of magnetic fields. The calculation incorporating Landau levels shows that there is no qualitative change of the reentrant behavior.

  4. The application of Regge calculus to quantum gravity and quantum field theory in a curved background

    International Nuclear Information System (INIS)

    Warner, N.P.

    1982-01-01

    The application of Regge calculus to quantum gravity and quantum field theory in a curved background is discussed. A discrete form of exterior differential calculus is developed, and this is used to obtain Laplacians for p-forms on the Regge manifold. To assess the accuracy of these approximations, the eigenvalues of the discrete Laplacians were calculated for the regular tesselations of S 2 and S 3 . The results indicate that the methods obtained in this paper may be used in curved space-times with an accuracy comparing with that obtained in lattice gauge theories on a flat background. It also becomes evident that Regge calculus provides particularly suitable lattices for Monte-Carlo techniques. (author)

  5. Quantum spaces, central extensions of Lie groups and related quantum field theories

    Science.gov (United States)

    Poulain, Timothé; Wallet, Jean-Christophe

    2018-02-01

    Quantum spaces with su(2) noncommutativity can be modelled by using a family of SO(3)-equivariant differential *-representations. The quantization maps are determined from the combination of the Wigner theorem for SU(2) with the polar decomposition of the quantized plane waves. A tracial star-product, equivalent to the Kontsevich product for the Poisson manifold dual to su(2) is obtained from a subfamily of differential *-representations. Noncommutative (scalar) field theories free from UV/IR mixing and whose commutative limit coincides with the usual ϕ 4 theory on ℛ3 are presented. A generalization of the construction to semi-simple possibly non simply connected Lie groups based on their central extensions by suitable abelian Lie groups is discussed. Based on a talk presented by Poulain T at the XXVth International Conference on Integrable Systems and Quantum symmetries (ISQS-25), Prague, June 6-10 2017.

  6. Magnetic Fields in neutron stars : A theoretical perspective

    NARCIS (Netherlands)

    Reisenegger, A.; Prieto, J.; Benguria, R.; Lai, D.; Araya, P.

    2005-01-01

    Abstract: We present our view of the main physical ingredients determining the evolution of neutron star magnetic fields. This includes the basic properties of neutron star matter, possible scenarios for the origin of the magnetic field, constraints and mechanisms for its evolution, and a discussion

  7. Determining Student Competency in Field Placements: An Emerging Theoretical Model

    Science.gov (United States)

    Salm, Twyla L.; Johner, Randy; Luhanga, Florence

    2016-01-01

    This paper describes a qualitative case study that explores how twenty-three field advisors, representing three human service professions including education, nursing, and social work, experience the process of assessment with students who are struggling to meet minimum competencies in field placements. Five themes emerged from the analysis of…

  8. Quantum Lifshitz Field Theory of a Frustrated Ferromagnet.

    Science.gov (United States)

    Balents, Leon; Starykh, Oleg A

    2016-04-29

    We propose a universal nonlinear sigma model field theory for one-dimensional frustrated ferromagnets, which applies in the vicinity of a "quantum Lifshitz point," at which the ferromagnetic state develops a spin wave instability. We investigate the phase diagram resulting from perturbations of the exchange and of magnetic field away from the Lifshitz point, and uncover a rich structure with two distinct regimes of different properties, depending upon the value of a marginal, dimensionless, parameter of the theory. In the regime relevant for one-dimensional systems with low spin, we find a metamagnetic transition line to a vector chiral phase. This line terminates in a critical end point, beyond which there is at least one multipolar or "spin nematic" phase. We show that the field theory is asymptotically exactly soluble near the Lifshitz point.

  9. Coarse grainings and irreversibility in quantum field theory

    International Nuclear Information System (INIS)

    Anastopoulos, C.

    1997-01-01

    In this paper we are interested in studying coarse graining in field theories using the language of quantum open systems. Motivated by the ideas of Hu and Calzetta on correlation histories we employ the Zwanzig projection technique to obtain evolution equations for relevant observables in self-interacting scalar field theories. Our coarse-graining operation consists in concentrating solely on the evolution of the correlation functions of degree less than n, a treatment which corresponds to the familiar truncation of the BBKGY hierarchy at the nth level. We derive the equations governing the evolution of mean-field and two-point functions thus identifying the terms corresponding to dissipation and noise. We discuss possible applications of our formalism, the emergence of classical behavior, and the connection to the decoherent histories framework. copyright 1997 The American Physical Society

  10. Crystal orientation effects on wurtzite quantum well electromechanical fields

    DEFF Research Database (Denmark)

    Duggen, Lars; Willatzen, Morten

    2010-01-01

    in the literature for semiconductors, is inaccurate for ZnO/MgZnO heterostructures where shear-strain components play an important role. An interesting observation is that a growth direction apart from [1̅ 21̅ 0] exists for which the electric field in the quantum well region becomes zero. This is important for, e......A one-dimensional continuum model for calculating strain and electric field in wurtzite semiconductor heterostructures with arbitrary crystal orientation is presented and applied to GaN/AlGaN and ZnO/MgZnO heterostructure combinations. The model is self-consistent involving feedback couplings...... of spontaneous polarization, strain, and electric field. Significant differences between fully coupled and semicoupled models are found for the longitudinal and shear-strain components as a function of the crystal-growth direction. In particular, we find that the semicoupled model, typically used...

  11. A calculational scheme for nonequilibrium quantum field system

    International Nuclear Information System (INIS)

    Yamanaka, Y.

    1991-01-01

    A new calculational scheme is presented for interacting nonequi-librium time dependent quantum field systems within the framework of thermo field dynamics (TFD), taking account of the fact that the thermal vacuum should go through many inequivalent state vector spaces. A para-meter parametrizing various state vector spaces has to be introduced and plays a role of new time-variable. Thus we have double-time TFD. The 2 requirements in this double-time TFD are imposed to establish a quasi-particle picture to get an attainable scheme of perturbative calculation : the existence of the spectral representation for the full propagator and the diagonalization of the quasi-particle Hamiltonian. The 1st condition turns out to amount to the existence of local-time tempera-ture. The 2nd condition leads to the master equation for the number density. This formalism is applied to high-energy heavy ion collision process. The very fundamental question is then how the thermodynamical properties such as heat and temperature appear in such an isolated system. This double-time TFD, suitable for isolated thermal systems of quantum fields, can handle the situation from the beginning of the process. (author). 24 refs.; 1 fig

  12. Quantum Conformal Algebras and Closed Conformal Field Theory

    CERN Document Server

    Anselmi, D

    1999-01-01

    We investigate the quantum conformal algebras of N=2 and N=1 supersymmetric gauge theories. Phenomena occurring at strong coupling are analysed using the Nachtmann theorem and very general, model-independent, arguments. The results lead us to introduce a novel class of conformal field theories, identified by a closed quantum conformal algebra. We conjecture that they are the exact solution to the strongly coupled large-N_c limit of the open conformal field theories. We study the basic properties of closed conformal field theory and work out the operator product expansion of the conserved current multiplet T. The OPE structure is uniquely determined by two central charges, c and a. The multiplet T does not contain just the stress-tensor, but also R-currents and finite mass operators. For this reason, the ratio c/a is different from 1. On the other hand, an open algebra contains an infinite tower of non-conserved currents, organized in pairs and singlets with respect to renormalization mixing. T mixes with a se...

  13. Tensor fields on orbits of quantum states and applications

    Energy Technology Data Exchange (ETDEWEB)

    Volkert, Georg Friedrich

    2010-07-19

    On classical Lie groups, which act by means of a unitary representation on finite dimensional Hilbert spaces H, we identify two classes of tensor field constructions. First, as pull-back tensor fields of order two from modified Hermitian tensor fields, constructed on Hilbert spaces by means of the property of having the vertical distributions of the C{sub 0}-principal bundle H{sub 0} {yields} P(H) over the projective Hilbert space P(H) in the kernel. And second, directly constructed on the Lie group, as left-invariant representation-dependent operator-valued tensor fields (LIROVTs) of arbitrary order being evaluated on a quantum state. Within the NP-hard problem of deciding whether a given state in a n-level bi-partite quantum system is entangled or separable (Gurvits, 2003), we show that both tensor field constructions admit a geometric approach to this problem, which evades the traditional ambiguity on defining metrical structures on the convex set of mixed states. In particular by considering manifolds associated to orbits passing through a selected state when acted upon by the local unitary group U(n) x U(n) of Schmidt coefficient decomposition inducing transformations, we find the following results: In the case of pure states we show that Schmidt-equivalence classes which are Lagrangian submanifolds define maximal entangled states. This implies a stronger statement as the one proposed by Bengtsson (2007). Moreover, Riemannian pull-back tensor fields split on orbits of separable states and provide a quantitative characterization of entanglement which recover the entanglement measure proposed by Schlienz and Mahler (1995). In the case of mixed states we highlight a relation between LIROVTs of order two and a class of computable separability criteria based on the Bloch-representation (de Vicente, 2007). (orig.)

  14. Galilei-invariant quantum field theories with pair interaction review

    International Nuclear Information System (INIS)

    Narnhofer, H.; Thirring, W.

    1990-01-01

    We exhibit a class of quantum field theories where particles interact with pair potentials and for which the time evolution exists in the Heisenberg representation. The essential condition for existence is the stability in the thermodynamic sense and this is achieved by having the interaction fall off with the relative momenta of the particles. This can be done in a Galilei-invariant manner. We show that these systems have some mixing behaviour which one postulates in ergodic theory but difficult to prove for classical systems. (Authors) 59 refs

  15. Quantum communication network utilizing quadripartite entangled states of optical field

    International Nuclear Information System (INIS)

    Shen Heng; Su Xiaolong; Jia Xiaojun; Xie Changde

    2009-01-01

    We propose two types of quantum dense coding communication networks with optical continuous variables, in which a quadripartite entangled state of the optical field with totally three-party correlations of quadrature amplitudes is utilized. In the networks, the exchange of information between any two participants can be manipulated by one or two of the remaining participants. The channel capacities for a variety of communication protocols are numerically calculated. Due to the fact that the quadripartite entangled states applied in the communication systems have been successfully prepared already in the laboratory, the proposed schemes are experimentally accessible at present.

  16. Yang-Baxter algebra - Integrable systems - Conformal quantum field theories

    International Nuclear Information System (INIS)

    Karowski, M.

    1989-01-01

    This series of lectures is based on investigations [1,2] of finite-size corrections for the six-vertex model by means of Bethe ansatz methods. In addition a review on applications of Yang-Baxter algebras and an introduction to the theory of integrable systems and the algebraic Bethe ansatz is presented. A Θ-vacuum like angle appearing in the RSOS-models is discussed. The continuum limit in the critical case of these statistical models is performed to obtain the minimal models of conformal quantum field theory. (author)

  17. White Noise and Heating of Open Quantum Field Fermi Systems

    CERN Document Server

    Abrikosov, A A

    1993-01-01

    I study the time evolution of the density matrices of quantum Fermi systems interacting with classic external Fermi fields. This interaction either changes the temperature of the system or it affects the density of particles. For relativistic Dirac fermions, variations of temperature lead to creation (annihilation) of particle - antiparticle pairs. The change of the density (or of the chemical potential) indicates the existence of the incoming (outgoing) flux of fermions from (to) the bath. These changes are independent for the different modes and in order to model the thermalization one should adjust the spectrum of the noise. The linear time dependences of the densities of particles are characteristic for all the processes.

  18. Equivariant topological quantum field theory and symmetry protected topological phases

    Energy Technology Data Exchange (ETDEWEB)

    Kapustin, Anton [Division of Physics, California Institute of Technology,1200 E California Blvd, Pasadena, CA, 91125 (United States); Turzillo, Alex [Simons Center for Geometry and Physics, State University of New York,Stony Brook, NY, 11794 (United States)

    2017-03-01

    Short-Range Entangled topological phases of matter are closely related to Topological Quantum Field Theory. We use this connection to classify Symmetry Protected Topological phases in low dimensions, including the case when the symmetry involves time-reversal. To accomplish this, we generalize Turaev’s description of equivariant TQFT to the unoriented case. We show that invertible unoriented equivariant TQFTs in one or fewer spatial dimensions are classified by twisted group cohomology, in agreement with the proposal of Chen, Gu, Liu and Wen. We also show that invertible oriented equivariant TQFTs in spatial dimension two or fewer are classified by ordinary group cohomology.

  19. Exact integrability in quantum field theory and statistical systems

    International Nuclear Information System (INIS)

    Thacker, H.B.

    1981-01-01

    The properties of exactly integrable two-dimensional quantum systems are reviewed and discussed. The nature of exact integrability as a physical phenomenon and various aspects of the mathematical formalism are explored by discussing several examples, including detailed treatments of the nonlinear Schroedinger (delta-function gas) model, the massive Thirring model, and the six-vertex (ice) model. The diagonalization of a Hamiltonian by Bethe's Ansatz is illustrated for the nonlinear Schroedinger model, and the integral equation method of Lieb for obtaining the spectrum of the many-body system from periodic boundary conditions is reviewed. Similar methods are applied to the massive Thirring model, where the fermion-antifermion and bound-state spectrum are obtained explicitly by the integral equation method. After a brief review of the classical inverse scattering method, the quantum inverse method for the nonlinear Schroedinger model is introduced and shown to be an algebraization of the Bethe Ansatz technique. In the quantum inverse method, an auxiliary linear problem is used to define nonlocal operators which are functionals of the original local field on a fixed-time string of arbitrary length. The particular operators for which the string is infinitely long (free boundary conditions) or forms a closed loop around a cylinder (periodic boundary conditions) correspond to the quantized scattering data and have a special significance. One of them creates the Bethe eigenstates, while the other is the generating function for an infinite number of conservation laws. The analogous operators on a lattice are constructed for the symmetric six-vertex model, where the object which corresponds to a solution of the auxiliary linear problem is a string of vertices contracted over horizontal links (arrows). The relationship between the quantum inverse method and the transfer matrix formalism is exhibited

  20. Tensorial spacetime geometries and background-independent quantum field theory

    International Nuclear Information System (INIS)

    Raetzel, Dennis

    2012-01-01

    Famously, Einstein read off the geometry of spacetime from Maxwell's equations. Today, we take this geometry that serious that our fundamental theory of matter, the standard model of particle physics, is based on it. However, it seems that there is a gap in our understanding if it comes to the physics outside of the solar system. Independent surveys show that we need concepts like dark matter and dark energy to make our models fit with the observations. But these concepts do not fit in the standard model of particle physics. To overcome this problem, at least, we have to be open to matter fields with kinematics and dynamics beyond the standard model. But these matter fields might then very well correspond to different spacetime geometries. This is the basis of this thesis: it studies the underlying spacetime geometries and ventures into the quantization of those matter fields independently of any background geometry. In the first part of this thesis, conditions are identified that a general tensorial geometry must fulfill to serve as a viable spacetime structure. Kinematics of massless and massive point particles on such geometries are introduced and the physical implications are investigated. Additionally, field equations for massive matter fields are constructed like for example a modified Dirac equation. In the second part, a background independent formulation of quantum field theory, the general boundary formulation, is reviewed. The general boundary formulation is then applied to the Unruh effect as a testing ground and first attempts are made to quantize massive matter fields on tensorial spacetimes.

  1. Exponential Speedup of Quantum Annealing by Inhomogeneous Driving of the Transverse Field

    Science.gov (United States)

    Susa, Yuki; Yamashiro, Yu; Yamamoto, Masayuki; Nishimori, Hidetoshi

    2018-02-01

    We show, for quantum annealing, that a certain type of inhomogeneous driving of the transverse field erases first-order quantum phase transitions in the p-body interacting mean-field-type model with and without longitudinal random field. Since a first-order phase transition poses a serious difficulty for quantum annealing (adiabatic quantum computing) due to the exponentially small energy gap, the removal of first-order transitions means an exponential speedup of the annealing process. The present method may serve as a simple protocol for the performance enhancement of quantum annealing, complementary to non-stoquastic Hamiltonians.

  2. The vacuum structure, special relativity theory and quantum mechanics revisited: a field theory-no-geometry approach

    International Nuclear Information System (INIS)

    Bogolubov, N.N. Jr.; Prykarpatsky, A.K.; Ufuk Taneri

    2008-07-01

    The main fundamental principles characterizing the vacuum field structure are formulated and the modeling of the related vacuum medium and charged point particle dynamics by means of de- vised field theoretic tools are analyzed. The Maxwell electrodynamic theory is revisited and newly derived from the suggested vacuum field structure principles and the classical special relativity theory relationship between the energy and the corresponding point particle mass is revisited and newly obtained. The Lorentz force expression with respect to arbitrary non-inertial reference frames is revisited and discussed in detail, and some new interpretations of relations between the special relativity theory and quantum mechanics are presented. The famous quantum-mechanical Schroedinger type equations for a relativistic point particle in the external potential and magnetic fields within the quasiclassical approximation as the Planck constant (h/2π) → 0 and the light velocity c → ∞ are obtained. (author)

  3. Quantum physics meets the philosophy of mind. New essays on the mind-body relation in quantum-theoretical perspective

    International Nuclear Information System (INIS)

    Corradini, Antonella; Meixner, Uwe

    2014-01-01

    Quantum physics, in contrast to classical physics, allows non-locality and indeterminism in nature. Moreover, the role of the observer seems indispensable in quantum physics. In fact, quantum physics, unlike classical physics, suggests a metaphysics that is not physicalism (which is today's official metaphysical doctrine). As is well known, physicalism implies a reductive position in the philosophy of mind, specifically in its two core areas, the philosophy of consciousness and the philosophy of action. Quantum physics, in contrast, is compatible with psychological non-reductionism, and actually seems to support it. The essays in this book explore, from various points of view, the possibilities of basing a non-reductive philosophy of mind on quantum physics. In doing so, they not only engage with the ontological and epistemological aspects of the question but also with the neurophysiological ones.

  4. Quantum physics meets the philosophy of mind. New essays on the mind-body relation in quantum-theoretical perspective

    Energy Technology Data Exchange (ETDEWEB)

    Corradini, Antonella [Catholic Univ., Milan (Italy); Meixner, Uwe (ed.) [Augsburg Univ. (Germany)

    2014-07-01

    Quantum physics, in contrast to classical physics, allows non-locality and indeterminism in nature. Moreover, the role of the observer seems indispensable in quantum physics. In fact, quantum physics, unlike classical physics, suggests a metaphysics that is not physicalism (which is today's official metaphysical doctrine). As is well known, physicalism implies a reductive position in the philosophy of mind, specifically in its two core areas, the philosophy of consciousness and the philosophy of action. Quantum physics, in contrast, is compatible with psychological non-reductionism, and actually seems to support it. The essays in this book explore, from various points of view, the possibilities of basing a non-reductive philosophy of mind on quantum physics. In doing so, they not only engage with the ontological and epistemological aspects of the question but also with the neurophysiological ones.

  5. Simple theoretical analysis of the photoemission from quantum confined effective mass superlattices of optoelectronic materials

    Directory of Open Access Journals (Sweden)

    Debashis De

    2011-07-01

    Full Text Available The photoemission from quantum wires and dots of effective mass superlattices of optoelectronic materials was investigated on the basis of newly formulated electron energy spectra, in the presence of external light waves, which controls the transport properties of ultra-small electronic devices under intense radiation. The effect of magnetic quantization on the photoemission from the aforementioned superlattices, together with quantum well superlattices under magnetic quantization, has also been investigated in this regard. It appears, taking HgTe/Hg1−xCdxTe and InxGa1−xAs/InP effective mass superlattices, that the photoemission from these quantized structures is enhanced with increasing photon energy in quantized steps and shows oscillatory dependences with the increasing carrier concentration. In addition, the photoemission decreases with increasing light intensity and wavelength as well as with increasing thickness exhibiting oscillatory spikes. The strong dependence of the photoemission on the light intensity reflects the direct signature of light waves on the carrier energy spectra. The content of this paper finds six different applications in the fields of low dimensional systems in general.

  6. Quantum cryptography

    CERN Document Server

    Gilbert, Gerald; Hamrick, Michael

    2013-01-01

    This book provides a detailed account of the theory and practice of quantum cryptography. Suitable as the basis for a course in the subject at the graduate level, it crosses the disciplines of physics, mathematics, computer science and engineering. The theoretical and experimental aspects of the subject are derived from first principles, and attention is devoted to the practical development of realistic quantum communications systems. The book also includes a comprehensive analysis of practical quantum cryptography systems implemented in actual physical environments via either free-space or fiber-optic cable quantum channels. This book will be a valuable resource for graduate students, as well as professional scientists and engineers, who desire an introduction to the field that will enable them to undertake research in quantum cryptography. It will also be a useful reference for researchers who are already active in the field, and for academic faculty members who are teaching courses in quantum information s...

  7. Quantum fields on manifolds: PCT and gravitationally induced thermal states

    International Nuclear Information System (INIS)

    Sewell, G.L.

    1982-01-01

    We formulate an axiomatic scheme, designed to provide a framework for a general, rigorous theory of relativistic quantum fields on a class of manifolds, that includes Kruskal's extension of Schwarzchild space-time, as well as Minkowski space-time. The scheme is an adaptation of Wightman's to this class of manifolds. We infer from it that, given an arbitrary field (in general, interacting) on a manifold X, the restriction of the field to a certain open submanifold X/sup( + ), whose boundaries are event horizons, satisfies the Kubo--Martin--Schwinger (KMS) thermal equilibrium conditions. This amounts to a rigorous, model-independent proof of a generalized Hawking--Unruh effect. Further, in cases where the field enjoys a certain PCT symmetry, the conjugation governing the KMS condition is just the PCT operator. The key to these results is an analogue, that we prove, of the Bisognano--Wichmann theorem [J. Math. Phys. 17, (1976), Theorem 1]. We also construct an alternative scheme by replacing a regularity condition at an event horizon by the assumption that the field in X/sup( + ) is in a ground, rather then a thermal, state. We show that, in this case, the observables in X/sup( + ) are uncorrelated to those in its causal complement, X/sup( - ), and thus that the event horizons act as physical barriers. Finally, we argue that the choice between the two schemes must be dictated by the prevailing conditions governing the state of the field

  8. Field Effect Optoelectronic Modulation of Quantum-Confined Carriers in Black Phosphorus.

    Science.gov (United States)

    Whitney, William S; Sherrott, Michelle C; Jariwala, Deep; Lin, Wei-Hsiang; Bechtel, Hans A; Rossman, George R; Atwater, Harry A

    2017-01-11

    We report measurements of the infrared optical response of thin black phosphorus under field-effect modulation. We interpret the observed spectral changes as a combination of an ambipolar Burstein-Moss (BM) shift of the absorption edge due to band-filling under gate control, and a quantum confined Franz-Keldysh (QCFK) effect, phenomena that have been proposed theoretically to occur for black phosphorus under an applied electric field. Distinct optical responses are observed depending on the flake thickness and starting carrier concentration. Transmission extinction modulation amplitudes of more than two percent are observed, suggesting the potential for use of black phosphorus as an active material in mid-infrared optoelectronic modulator applications.

  9. Preheating in an asymptotically safe quantum field theory

    DEFF Research Database (Denmark)

    Svendsen, Ole; Moghaddam, Hossein Bazrafshan; Brandenberger, Robert

    2016-01-01

    We consider reheating in a class of asymptotically safe quantum field theories recently studied in [D. F. Litim and F. Sannino, Asymptotic safety guaranteed, J. High Energy Phys. 12 (2014) 178; D. F. Litim, M. Mojaza, and F. Sannino, Vacuum stability of asymptotically safe gauge-Yukawa theories, J...... fluctuations induced by the parametrically amplified entropy modes do not exceed the upper observational bounds puts a lower bound on the number of fields which the model followed in [D. F. Litim and F. Sannino, Asymptotic safety guaranteed, J. High Energy Phys. 12 (2014) 178; D. F. Litim, M. Mojaza, and F....... Sannino, Vacuum stability of asymptotically safe gauge-Yukawa theories, J. High Energy Phys. 01 (2016) 081] must contain. This bound also depends on the total number of e-foldings of the inflationary phase....

  10. Indefinite-metric quantum field theory of general relativity

    International Nuclear Information System (INIS)

    Nakanishi, Noboru

    1978-01-01

    Quantum field theory of Einstein's general relativity is formulated in the indefinitemetric Hilbert space in such a way that asymptotic fields are manifestly Lorentz covariant and the physical S-matrix is unitary. The general coordinate transformation is transcribed into a q-number transformation, called the BRS transformation. Its abstract definition is presented on the basis of the BRS transformation for the Yang-Mills theory. The BRS transformation for general relativity is then explicitly constructed. The gauge-fixing Lagrangian density and the Faddeev-Popov one are introduced in such a way that their sum behaves like a scalar density under the BRS transformation. One can then proceed in the same way as in the Kugo-Ojima formalism of the Yang-Mills theory to establish the unitarity of the physical S-matrix. (author)

  11. Non-local charges in local quantum field theory

    International Nuclear Information System (INIS)

    Buchholz, D.; Lopuszanski, J.T.; Rabsztyn, S.

    1985-05-01

    Non-local charges are studied in the general setting of local quantum field theory. It is shown, that these charges can be represented as polynomials in the incoming respectively outgoing fields with coefficients (kernels) which are subject to specific constraints. For the restricted class of models of a scalar, massive, self interacting particle in four dimensions, a more detailed analysis shows that all non-local charges of the generic type (genus 2) are products of generators of the Poincare group. This analysis, which is based on the macroscopic causality properties of the S-matrix, seems to indicate that less trivial examples of non-local charges can only exist in two dimensions. (orig.)

  12. Quantum field theory on discrete space-time. II

    International Nuclear Information System (INIS)

    Yamamoto, H.

    1985-01-01

    A quantum field theory of bosons and fermions is formulated on discrete Lorentz space-time of four dimensions. The minimum intervals of space and time are assumed to have different values in this paper. As a result the difficulties encountered in the previous paper (complex energy, incompleteness of solutions, and inequivalence between phase representation and momentum representation) are removed. The problem in formulating a field theory of fermions is solved by introducing a new operator and considering a theorem of translation invariance. Any matrix element given by a Feynman diagram is calculated in this theory to give a finite value regardless of the kinds of particles concerned (massive and/or massless bosons and/or fermions)

  13. ELECTRON HOLOGRAPHY OF ELECTROMAGNETIC FIELDS - RECENT THEORETICAL ADVANCES.

    Energy Technology Data Exchange (ETDEWEB)

    BELEGGIA,M.; POZZI, G.; TONOMURA, A.

    2007-01-01

    It has been shown in this work that the Fourier space approach can be fruitfully applied to the calculation of the fields and the associated electron optical phase shift of several magnetic and electrostatic structures, like superconducting vortices in conventional and high-T{sub c} superconductors, reverse biased p-n junctions, magnetic domains and nanoparticles. In all these cases, this novel approach has led to unexpected but extremely interesting results, very often expressed in analytical form, which allow the quantitative and reliable interpretation of the experimental data collected by means of electron holography or of more conventional Lorentz microscopy techniques. Moreover, it is worth recalling that whenever long-range electromagnetic fields are involved, a physical model of the object under investigation is necessary in order to take into account correctly the perturbation of the reference wave induced by the tail of the field protruding into the vacuum. For these reasons, we believe that the Fourier space approach for phase computations we have introduced and discussed in this chapter will represent an invaluable tool for the investigation of electromagnetic fields at the meso- and nano-scale.

  14. Theoretical models of magnetic field line merging. I

    International Nuclear Information System (INIS)

    Vasyliunas, V.M.

    1975-01-01

    Models of magnetic field line merging that consider processes in a limited region around the magnetic X line, within which the external magnetic fields are roughly uniform and antiparallel, are reviewed. Part I describes the concept of magnetic merging and then considers the models based on a hydromagnetic approach. The models developed by Sweet and Parker, by Petschek, and by Sonnerup and Yeh and Axford are shown to be fundamentally consistent, representing different aspects of the same problem. The model of Sweet and Parker describes the small region around the neutral line where magnetic field diffusion is the dominant process. The inclusion of inertial as well as finite resistivity effects allows an extension of their model to collisionless plasmas. Petschek's model represents a system with a boundary condition of uniform field at the sides; it has been extended and formulated in a mathematically precise manner. The nonsingular model of Sonnerup and of Yeh and Axford has special boundary conditions at the sides producing localized slow mode MHD expansion fans in the external flow; the singular models and the compressible similarity models are physically unrealizable. The maximum merging rate corresponds to flow into the diffusion region of the local Alfven speed, which, however, can be made arbitrarily large by slow mode MHD expansion if suitable boundary condi []ions are present. (auth)

  15. Gauge-fields and integrated quantum-classical theory

    Energy Technology Data Exchange (ETDEWEB)

    Stapp, H.P.

    1986-01-01

    Physical situations in which quantum systems communicate continuously to their classically described environment are not covered by contemporary quantum theory, which requires a temporary separation of quantum degrees of freedom from classical ones. A generalization would be needed to cover these situations. An incomplete proposal is advanced for combining the quantum and classical degrees of freedom into a unified objective description. It is based on the use of certain quantum-classical structures of light that arise from gauge invariance to coordinate the quantum and classical degrees of freedom. Also discussed is the question of where experimenters should look to find phenomena pertaining to the quantum-classical connection. 17 refs.

  16. Quantum phases for a charged particle and electric/magnetic dipole in an electromagnetic field

    Science.gov (United States)

    Kholmetskii, Alexander; Yarman, Tolga

    2017-11-01

    We point out that the known quantum phases for an electric/magnetic dipole moving in an electromagnetic field must be composed from more fundamental quantum phases emerging for moving elementary charges. Using this idea, we have found two new fundamental quantum phases, next to the known magnetic and electric Aharonov-Bohm phases, and discuss their general properties and physical meaning.

  17. Quantum Mechanical Calculations in Collaborations with Experimental Chemistry: The Theoretical Organic Chemistry Perspective

    Science.gov (United States)

    Nguyen, Quynh Nhu Ngoc

    synthesized peptides, dynamic simulations were used to sample a large conformational space, generating diverse conformer libraries. Quantum mechanical calculations were then used to determine the relative energies between the conformers, and to compute theoretical NMR data, which were then compared to the experimental values, to determine the best match conformers. Hydropersulfides are commonly found among many mammalian systems, and has recently gained more interest due to their greater nucleophilicity and reducing capacity compared to the related thiols. A series of quantum mechanical calculations were performed for small sulfur-containing molecules in order to help understand these biological compounds. First part of this chapter explores the basics of chemical properties and reactivity of hydropersulfides. The later sections further discuss the redox component of RSSH in generation of the radical RSS, which was found to be unreactive in the presence of O 2 and NO. Modeling the formation of these natural products in the absence of the enzymes has many of its own limitation, but understanding the inherent reactivity of the substrates could be beneficial to future enzymatic studies. Density functional theory calculations of mechanism of caryolene featured one mechanism with a base-catalyzed deprotonation/reprotonation sequence, while the other higher-energy mechanism involved intramolecular proton transfer and a secondary carbocation minimum. This result suggested the role of the enzyme in helping to avoid the secondary carbocation. Both pathways bypassed the concerted suprafacial/suprafacial [2+2] cycloadditions, which were not in violation of orbital symmetry due to their asynchronicity. Quantum mechanical calculations were used to determine theoretical 1H and 13C chemical shifts, which were then compared to the experimental NMR data to assign relative configurations for isohirsut-1-ene, isohirsut-4-ene, and tsukubadiene, which were previously isolated from engineered

  18. A theoretical investigation of quantum confinement effects in heterojunction silicon solar cells

    Science.gov (United States)

    Bashiri, H.; Karami, M. A.; Mohammadnejad, Sh.

    2018-03-01

    The effect of quantum confinement potential on the performance of a silicon-based heterojunction solar cell with an intrinsic thin-layer of a-Si:H is studied using numerical simulations. The presence of defects at c-Si/a-Si:H interface is studied quantitatively and, an analytical solution is investigated to interpret experimental results. Moreover, the impact of defect density at c-Si/a-Si:H interface on the solar cell operation is explained. By the use of a theoretical model, the effect of intrinsic amorphous layer thickness, and interface defect density on quasi-Fermi level are studied and the mechanisms of open circuit voltage ( V oc ) variations, are interpreted successfully. It is shown that the best performance of heterojunction silicon solar cell with a single passivation layer is obtained when the thickness of (i)a-Si:H is 3-9 nm and heterojunction interface defect density is lower than 1010 cm-2 eV-1.

  19. On generally covariant quantum field theory and generalized causal and dynamical structures

    International Nuclear Information System (INIS)

    Bannier, U.

    1988-01-01

    We give an example of a generally covariant quasilocal algebra associated with the massive free field. Maximal, two-sided ideals of this algebra are algebraic representatives of external metric fields. In some sense, this algebra may be regarded as a concrete realization of Ekstein's ideas of presymmetry in quantum field theory. Using ideas from our example and from usual algebraic quantum field theory, we discuss a generalized scheme, in which maximal ideals are viewed as algebraic representatives of dynamical equations or Lagrangians. The considered frame is no quantum gravity, but may lead to further insight into the relation between quantum theory and space-time geometry. (orig.)

  20. Quantum field theory and gravity in causal sets

    Science.gov (United States)

    Sverdlov, Roman M.

    Causal set is a model of space time that allows to reconcile discreteness and manifest relativistic invariance. This is done by viewing space time as finite, partially ordered set. The elements of the set are viewed as points of space time, or events; the partial ordering between them is viewed as causal relations. It has been shown that, in discrete scenario, the information about causal relations between events can, indeed, approximate the metric. The goal of this thesis is to introduce matter fields and their Lagrangians into causal set context. This is a two step process. The first step is to re-define gauge fields, gravity, and distances in such a way that no reference to Lorentz index is made. This is done by defining gauge fields as two-point real valued functions, and gravitational field as causal structure itself. Once the above is done, Lagrangians have to be defined in a way that they don't refer to Lorentzian indices either. This is done by introducing a notion of type 1 and type 2 Lagrangian generators, coupled with respective machinery that "translates" each generator into corresponding Lagrangian. The fields that are subject to these generators are, respectively, defined as type 1 and type 2. The main difference between two kinds of fields is the prediction of different behavior in different dimensions of type 2 fields. However, despite our inability to travel to different dimensions, gravity was shown to be type 2 based on the erroneous predictions of its 4-dimensional behavior if it was viewed as type 1. However, no erroneous predictions are made if non-gravitational fields are viewed as either type 1 or type 2, thus the nature of the latter is still an open question. Finally, an attempt was made to provide interpretation of quantum mechanics that would allow to limit fluctuations of causal structure to allow some topological background. However, due to its controversial nature, it is placed in the Appendix.